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 $188.68   3.129%   $194.5838   $194.58   $194.60   $194.60  
  Purchase #2 $37.31   5.198%   $39.2494   $39.25   $39.25   $39.20  
  Purchase #3 $144.27   13.245%   $163.3786   $163.38   $163.40   $163.40  
  Purchase #4 $46.78   5.853%   $49.518   $49.52   $49.50   $49.50  
  Purchase #5 $186.40   6.160%   $197.8822   $197.88   $197.90   $197.90  
  Purchase #6 $149.29   13.548%   $169.5158   $169.52   $169.50   $169.50  
  Purchase #7 $50.96   3.372%   $52.6784   $52.68   $52.70   $52.70  
  7 purchase totals = $803.69       $866.8062   $866.81   $866.85   $866.80