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 $66.96   13.589%   $76.0592   $76.06   $76.05   $76.10  
  Purchase #2 $217.88   7.249%   $233.6741   $233.67   $233.65   $233.70  
  Purchase #3 $80.88   12.675%   $91.1315   $91.13   $91.15   $91.10  
  Purchase #4 $203.35   10.604%   $224.9132   $224.91   $224.90   $224.90  
  Purchase #5 $199.79   12.546%   $224.8557   $224.86   $224.85   $224.90  
  Purchase #6 $188.61   12.410%   $212.0165   $212.02   $212.00   $212.00  
  Purchase #7 $41.30   12.312%   $46.3849   $46.38   $46.40   $46.40  
  7 purchase totals = $998.77       $1,109.0351   $1,109.03   $1,109.00   $1,109.10