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 $22.93   4.489%   $23.9593   $23.96   $23.95   $24.00  
  Purchase #2 $165.46   6.249%   $175.7996   $175.80   $175.80   $175.80  
  Purchase #3 $240.83   8.386%   $261.026   $261.03   $261.05   $261.00  
  Purchase #4 $139.36   12.587%   $156.9012   $156.90   $156.90   $156.90  
  Purchase #5 $224.71   10.290%   $247.8327   $247.83   $247.85   $247.80  
  Purchase #6 $238.46   13.346%   $270.2849   $270.28   $270.30   $270.30  
  Purchase #7 $174.65   10.699%   $193.3358   $193.34   $193.35   $193.30  
  7 purchase totals = $1,206.40       $1,329.1395   $1,329.14   $1,329.20   $1,329.10