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 $244.38   12.817%   $275.7022   $275.70   $275.70   $275.70  
  Purchase #2 $159.99   5.379%   $168.5959   $168.60   $168.60   $168.60  
  Purchase #3 $236.78   12.353%   $266.0294   $266.03   $266.05   $266.00  
  Purchase #4 $181.70   6.776%   $194.012   $194.01   $194.00   $194.00  
  Purchase #5 $215.57   6.217%   $228.972   $228.97   $228.95   $229.00  
  Purchase #6 $123.42   10.190%   $135.9965   $136.00   $136.00   $136.00  
  Purchase #7 $85.74   3.218%   $88.4991   $88.50   $88.50   $88.50  
  7 purchase totals = $1,247.58       $1,357.8071   $1,357.81   $1,357.80   $1,357.80