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 $244.96   6.819%   $261.6638   $261.66   $261.65   $261.70  
  Purchase #2 $225.65   9.579%   $247.265   $247.27   $247.25   $247.30  
  Purchase #3 $93.88   11.751%   $104.9118   $104.91   $104.90   $104.90  
  Purchase #4 $58.65   7.430%   $63.0077   $63.01   $63.00   $63.00  
  Purchase #5 $177.40   8.170%   $191.8936   $191.89   $191.90   $191.90  
  Purchase #6 $213.93   3.330%   $221.0539   $221.05   $221.05   $221.10  
  Purchase #7 $45.40   8.616%   $49.3117   $49.31   $49.30   $49.30  
  7 purchase totals = $1,059.87       $1,139.1075   $1,139.10   $1,139.05   $1,139.20