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 $62.67   8.587%   $68.0515   $68.05   $68.05   $68.10  
  Purchase #2 $184.29   7.160%   $197.4852   $197.49   $197.50   $197.50  
  Purchase #3 $150.76   10.175%   $166.0998   $166.10   $166.10   $166.10  
  Purchase #4 $178.61   13.568%   $202.8438   $202.84   $202.85   $202.80  
  Purchase #5 $48.74   7.399%   $52.3463   $52.35   $52.35   $52.30  
  Purchase #6 $55.38   12.720%   $62.4243   $62.42   $62.40   $62.40  
  Purchase #7 $165.47   13.759%   $188.237   $188.24   $188.25   $188.20  
  7 purchase totals = $845.92       $937.4879   $937.49   $937.50   $937.40