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 $125.27   13.303%   $141.9347   $141.93   $141.95   $141.90  
  Purchase #2 $172.26   7.369%   $184.9538   $184.95   $184.95   $185.00  
  Purchase #3 $161.73   4.442%   $168.914   $168.91   $168.90   $168.90  
  Purchase #4 $68.37   9.517%   $74.8768   $74.88   $74.90   $74.90  
  Purchase #5 $122.54   5.299%   $129.0334   $129.03   $129.05   $129.00  
  Purchase #6 $215.90   11.679%   $241.115   $241.12   $241.10   $241.10  
  Purchase #7 $75.53   7.621%   $81.2861   $81.29   $81.30   $81.30  
  7 purchase totals = $941.60       $1,022.1138   $1,022.11   $1,022.15   $1,022.10