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 $168.77   9.592%   $184.9584   $184.96   $184.95   $185.00  
  Purchase #2 $230.60   13.447%   $261.6088   $261.61   $261.60   $261.60  
  Purchase #3 $151.26   9.511%   $165.6463   $165.65   $165.65   $165.60  
  Purchase #4 $56.95   12.844%   $64.2647   $64.26   $64.25   $64.30  
  Purchase #5 $154.79   12.515%   $174.162   $174.16   $174.15   $174.20  
  Purchase #6 $240.90   13.657%   $273.7997   $273.80   $273.80   $273.80  
  Purchase #7 $117.35   10.219%   $129.342   $129.34   $129.35   $129.30  
  7 purchase totals = $1,120.62       $1,253.7819   $1,253.78   $1,253.75   $1,253.80