Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $132.71   12.472%   $149.2616   $149.26   $149.25   $149.30  
  Purchase #2 $125.71   10.799%   $139.2854   $139.29   $139.30   $139.30  
  Purchase #3 $104.75   10.722%   $115.9813   $115.98   $116.00   $116.00  
  Purchase #4 $163.86   11.460%   $182.6384   $182.64   $182.65   $182.60  
  Purchase #5 $223.68   4.866%   $234.5643   $234.56   $234.55   $234.60  
  Purchase #6 $135.43   8.687%   $147.1948   $147.19   $147.20   $147.20  
  Purchase #7 $120.28   4.737%   $125.9777   $125.98   $126.00   $126.00  
  7 purchase totals = $1,006.42       $1,094.9035   $1,094.90   $1,094.95   $1,095.00