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 $191.91   6.252%   $203.9082   $203.91   $203.90   $203.90  
  Purchase #2 $57.85   3.747%   $60.0176   $60.02   $60.00   $60.00  
  Purchase #3 $97.71   7.318%   $104.8604   $104.86   $104.85   $104.90  
  Purchase #4 $158.78   5.303%   $167.2001   $167.20   $167.20   $167.20  
  Purchase #5 $168.76   9.748%   $185.2107   $185.21   $185.20   $185.20  
  Purchase #6 $225.34   9.449%   $246.6324   $246.63   $246.65   $246.60  
  Purchase #7 $139.26   9.426%   $152.3866   $152.39   $152.40   $152.40  
  7 purchase totals = $1,039.61       $1,120.2160   $1,120.22   $1,120.20   $1,120.20