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 $61.35   9.156%   $66.9672   $66.97   $66.95   $67.00  
  Purchase #2 $17.53   11.468%   $19.5403   $19.54   $19.55   $19.50  
  Purchase #3 $95.63   6.677%   $102.0152   $102.02   $102.00   $102.00  
  Purchase #4 $191.58   9.316%   $209.4276   $209.43   $209.45   $209.40  
  Purchase #5 $127.95   9.263%   $139.802   $139.80   $139.80   $139.80  
  Purchase #6 $192.71   5.367%   $203.0527   $203.05   $203.05   $203.10  
  Purchase #7 $129.45   12.344%   $145.4293   $145.43   $145.45   $145.40  
  7 purchase totals = $816.20       $886.2343   $886.24   $886.25   $886.20