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 $85.46   12.531%   $96.169   $96.17   $96.15   $96.20  
  Purchase #2 $92.61   11.176%   $102.9601   $102.96   $102.95   $103.00  
  Purchase #3 $32.45   10.634%   $35.9007   $35.90   $35.90   $35.90  
  Purchase #4 $171.64   9.855%   $188.5551   $188.56   $188.55   $188.60  
  Purchase #5 $111.79   11.496%   $124.6414   $124.64   $124.65   $124.60  
  Purchase #6 $19.53   6.332%   $20.7666   $20.77   $20.75   $20.80  
  Purchase #7 $241.40   8.566%   $262.0783   $262.08   $262.10   $262.10  
  7 purchase totals = $754.88       $831.0712   $831.08   $831.05   $831.20