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 $232.90   6.421%   $247.8545   $247.85   $247.85   $247.90  
  Purchase #2 $149.54   8.129%   $161.6961   $161.70   $161.70   $161.70  
  Purchase #3 $58.73   13.131%   $66.4418   $66.44   $66.45   $66.40  
  Purchase #4 $193.85   13.380%   $219.7871   $219.79   $219.80   $219.80  
  Purchase #5 $132.80   7.845%   $143.2182   $143.22   $143.20   $143.20  
  Purchase #6 $29.78   6.627%   $31.7535   $31.75   $31.75   $31.80  
  Purchase #7 $54.38   12.512%   $61.184   $61.18   $61.20   $61.20  
  7 purchase totals = $851.98       $931.9352   $931.93   $931.95   $932.00