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 $46.52   8.785%   $50.6068   $50.61   $50.60   $50.60  
  Purchase #2 $241.49   12.411%   $271.4613   $271.46   $271.45   $271.50  
  Purchase #3 $126.88   12.273%   $142.452   $142.45   $142.45   $142.50  
  Purchase #4 $23.75   5.425%   $25.0384   $25.04   $25.05   $25.00  
  Purchase #5 $78.38   3.655%   $81.2448   $81.24   $81.25   $81.20  
  Purchase #6 $83.28   12.599%   $93.7724   $93.77   $93.75   $93.80  
  Purchase #7 $169.69   10.727%   $187.8926   $187.89   $187.90   $187.90  
  7 purchase totals = $769.99       $852.4683   $852.46   $852.45   $852.50