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 $66.29   10.577%   $73.3015   $73.30   $73.30   $73.30  
  Purchase #2 $169.71   5.869%   $179.6703   $179.67   $179.65   $179.70  
  Purchase #3 $168.90   5.122%   $177.5511   $177.55   $177.55   $177.60  
  Purchase #4 $182.26   5.190%   $191.7193   $191.72   $191.70   $191.70  
  Purchase #5 $241.60   6.182%   $256.5357   $256.54   $256.55   $256.50  
  Purchase #6 $203.98   8.630%   $221.5835   $221.58   $221.60   $221.60  
  Purchase #7 $250.60   10.231%   $276.2389   $276.24   $276.25   $276.20  
  7 purchase totals = $1,283.34       $1,376.6003   $1,376.60   $1,376.60   $1,376.60