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 $168.60   3.552%   $174.5887   $174.59   $174.60   $174.60  
  Purchase #2 $114.27   9.317%   $124.9165   $124.92   $124.90   $124.90  
  Purchase #3 $118.97   11.755%   $132.9549   $132.95   $132.95   $133.00  
  Purchase #4 $19.87   8.623%   $21.5834   $21.58   $21.60   $21.60  
  Purchase #5 $204.54   9.729%   $224.4397   $224.44   $224.45   $224.40  
  Purchase #6 $112.35   7.354%   $120.6122   $120.61   $120.60   $120.60  
  Purchase #7 $24.87   4.172%   $25.9076   $25.91   $25.90   $25.90  
  7 purchase totals = $763.47       $825.0030   $825.00   $825.00   $825.00