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 $217.84   9.219%   $237.9227   $237.92   $237.90   $237.90  
  Purchase #2 $189.77   7.274%   $203.5739   $203.57   $203.55   $203.60  
  Purchase #3 $46.66   4.770%   $48.8857   $48.89   $48.90   $48.90  
  Purchase #4 $194.27   5.397%   $204.7548   $204.75   $204.75   $204.80  
  Purchase #5 $136.82   5.673%   $144.5818   $144.58   $144.60   $144.60  
  Purchase #6 $216.28   5.709%   $228.6274   $228.63   $228.65   $228.60  
  Purchase #7 $116.63   7.665%   $125.5697   $125.57   $125.55   $125.60  
  7 purchase totals = $1,118.27       $1,193.9160   $1,193.91   $1,193.90   $1,194.00