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 $199.43   8.793%   $216.9659   $216.97   $216.95   $217.00  
  Purchase #2 $54.41   13.454%   $61.7303   $61.73   $61.75   $61.70  
  Purchase #3 $161.80   4.600%   $169.2428   $169.24   $169.25   $169.20  
  Purchase #4 $48.98   6.610%   $52.2176   $52.22   $52.20   $52.20  
  Purchase #5 $94.44   8.831%   $102.78   $102.78   $102.80   $102.80  
  Purchase #6 $141.70   3.398%   $146.515   $146.52   $146.50   $146.50  
  Purchase #7 $161.26   10.693%   $178.5035   $178.50   $178.50   $178.50  
  7 purchase totals = $862.02       $927.9551   $927.96   $927.95   $927.90