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 $112.65   12.268%   $126.4699   $126.47   $126.45   $126.50  
  Purchase #2 $84.85   4.351%   $88.5418   $88.54   $88.55   $88.50  
  Purchase #3 $154.75   5.577%   $163.3804   $163.38   $163.40   $163.40  
  Purchase #4 $118.91   3.162%   $122.6699   $122.67   $122.65   $122.70  
  Purchase #5 $138.88   9.449%   $152.0028   $152.00   $152.00   $152.00  
  Purchase #6 $105.34   12.385%   $118.3864   $118.39   $118.40   $118.40  
  Purchase #7 $210.41   6.340%   $223.75   $223.75   $223.75   $223.80  
  7 purchase totals = $925.79       $995.2012   $995.20   $995.20   $995.30