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 $138.26   6.121%   $146.7229   $146.72   $146.70   $146.70  
  Purchase #2 $95.86   7.198%   $102.76   $102.76   $102.75   $102.80  
  Purchase #3 $42.71   9.155%   $46.6201   $46.62   $46.60   $46.60  
  Purchase #4 $160.57   9.520%   $175.8563   $175.86   $175.85   $175.90  
  Purchase #5 $130.51   11.361%   $145.3372   $145.34   $145.35   $145.30  
  Purchase #6 $66.66   9.357%   $72.8974   $72.90   $72.90   $72.90  
  Purchase #7 $196.72   3.696%   $203.9908   $203.99   $204.00   $204.00  
  7 purchase totals = $831.29       $894.1847   $894.19   $894.15   $894.20