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 $203.74   11.472%   $227.1131   $227.11   $227.10   $227.10  
  Purchase #2 $246.97   8.471%   $267.8908   $267.89   $267.90   $267.90  
  Purchase #3 $46.33   8.127%   $50.0952   $50.10   $50.10   $50.10  
  Purchase #4 $93.37   13.308%   $105.7957   $105.80   $105.80   $105.80  
  Purchase #5 $150.39   8.791%   $163.6108   $163.61   $163.60   $163.60  
  Purchase #6 $12.39   9.870%   $13.6129   $13.61   $13.60   $13.60  
  Purchase #7 $126.49   8.399%   $137.1139   $137.11   $137.10   $137.10  
  7 purchase totals = $879.68       $965.2324   $965.23   $965.20   $965.20