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 $66.64   12.178%   $74.7554   $74.76   $74.75   $74.80  
  Purchase #2 $226.46   13.315%   $256.6131   $256.61   $256.60   $256.60  
  Purchase #3 $229.52   10.425%   $253.4475   $253.45   $253.45   $253.40  
  Purchase #4 $26.42   8.105%   $28.5613   $28.56   $28.55   $28.60  
  Purchase #5 $176.42   9.376%   $192.9611   $192.96   $192.95   $193.00  
  Purchase #6 $191.62   5.585%   $202.322   $202.32   $202.30   $202.30  
  Purchase #7 $143.48   10.774%   $158.9385   $158.94   $158.95   $158.90  
  7 purchase totals = $1,060.56       $1,167.5989   $1,167.60   $1,167.55   $1,167.60