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 $135.72   11.664%   $151.5504   $151.55   $151.55   $151.60  
  Purchase #2 $230.62   10.590%   $255.0427   $255.04   $255.05   $255.00  
  Purchase #3 $125.51   11.539%   $139.9926   $139.99   $140.00   $140.00  
  Purchase #4 $35.78   5.326%   $37.6856   $37.69   $37.70   $37.70  
  Purchase #5 $74.96   9.505%   $82.0849   $82.08   $82.10   $82.10  
  Purchase #6 $27.45   8.657%   $29.8263   $29.83   $29.85   $29.80  
  Purchase #7 $59.84   3.326%   $61.8303   $61.83   $61.85   $61.80  
  7 purchase totals = $689.88       $758.0128   $758.01   $758.10   $758.00