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 $182.98   6.854%   $195.5214   $195.52   $195.50   $195.50  
  Purchase #2 $61.73   9.420%   $67.545   $67.55   $67.55   $67.50  
  Purchase #3 $31.59   12.518%   $35.5444   $35.54   $35.55   $35.50  
  Purchase #4 $245.54   9.588%   $269.0824   $269.08   $269.10   $269.10  
  Purchase #5 $118.63   4.638%   $124.1321   $124.13   $124.15   $124.10  
  Purchase #6 $188.88   6.720%   $201.5727   $201.57   $201.55   $201.60  
  Purchase #7 $29.43   12.315%   $33.0543   $33.05   $33.05   $33.10  
  7 purchase totals = $858.78       $926.4523   $926.44   $926.45   $926.40