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 $187.38   10.738%   $207.5009   $207.50   $207.50   $207.50  
  Purchase #2 $56.83   4.148%   $59.1873   $59.19   $59.20   $59.20  
  Purchase #3 $148.69   12.667%   $167.5246   $167.52   $167.50   $167.50  
  Purchase #4 $176.29   10.303%   $194.4532   $194.45   $194.45   $194.50  
  Purchase #5 $154.96   6.528%   $165.0758   $165.08   $165.10   $165.10  
  Purchase #6 $247.90   5.202%   $260.7958   $260.80   $260.80   $260.80  
  Purchase #7 $193.63   6.568%   $206.3476   $206.35   $206.35   $206.30  
  7 purchase totals = $1,165.68       $1,260.8852   $1,260.89   $1,260.90   $1,260.90