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 $69.31   8.183%   $74.9816   $74.98   $75.00   $75.00  
  Purchase #2 $22.26   10.591%   $24.6176   $24.62   $24.60   $24.60  
  Purchase #3 $28.90   11.735%   $32.2914   $32.29   $32.30   $32.30  
  Purchase #4 $110.40   13.791%   $125.6253   $125.63   $125.65   $125.60  
  Purchase #5 $117.77   4.595%   $123.1815   $123.18   $123.20   $123.20  
  Purchase #6 $169.76   6.429%   $180.6739   $180.67   $180.65   $180.70  
  Purchase #7 $207.70   13.238%   $235.1953   $235.20   $235.20   $235.20  
  7 purchase totals = $726.10       $796.5666   $796.57   $796.60   $796.60