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 $106.74   11.506%   $119.0215   $119.02   $119.00   $119.00  
  Purchase #2 $8.86   3.352%   $9.157   $9.16   $9.15   $9.20  
  Purchase #3 $99.57   10.663%   $110.1871   $110.19   $110.20   $110.20  
  Purchase #4 $22.38   4.784%   $23.4507   $23.45   $23.45   $23.50  
  Purchase #5 $32.38   3.359%   $33.4676   $33.47   $33.45   $33.50  
  Purchase #6 $229.75   13.491%   $260.7456   $260.75   $260.75   $260.70  
  Purchase #7 $234.56   7.167%   $251.3709   $251.37   $251.35   $251.40  
  7 purchase totals = $734.24       $807.4004   $807.41   $807.35   $807.50