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 $119.54   11.249%   $132.9871   $132.99   $133.00   $133.00  
  Purchase #2 $225.53   8.788%   $245.3496   $245.35   $245.35   $245.30  
  Purchase #3 $148.47   10.257%   $163.6986   $163.70   $163.70   $163.70  
  Purchase #4 $133.73   10.503%   $147.7757   $147.78   $147.80   $147.80  
  Purchase #5 $68.62   3.616%   $71.1013   $71.10   $71.10   $71.10  
  Purchase #6 $84.39   10.257%   $93.0459   $93.05   $93.05   $93.00  
  Purchase #7 $181.40   5.472%   $191.3262   $191.33   $191.35   $191.30  
  7 purchase totals = $961.68       $1,045.2844   $1,045.30   $1,045.35   $1,045.20