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 $117.95   5.417%   $124.3394   $124.34   $124.35   $124.30  
  Purchase #2 $160.40   10.275%   $176.8811   $176.88   $176.90   $176.90  
  Purchase #3 $241.97   9.679%   $265.3903   $265.39   $265.40   $265.40  
  Purchase #4 $152.86   12.232%   $171.5578   $171.56   $171.55   $171.60  
  Purchase #5 $23.97   8.566%   $26.0233   $26.02   $26.00   $26.00  
  Purchase #6 $110.25   7.808%   $118.8583   $118.86   $118.85   $118.90  
  Purchase #7 $75.37   4.656%   $78.8792   $78.88   $78.90   $78.90  
  7 purchase totals = $882.77       $961.9294   $961.93   $961.95   $962.00