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 $108.86   9.302%   $118.9862   $118.99   $119.00   $119.00  
  Purchase #2 $237.77   8.108%   $257.0484   $257.05   $257.05   $257.00  
  Purchase #3 $56.41   13.737%   $64.159   $64.16   $64.15   $64.20  
  Purchase #4 $152.89   13.156%   $173.0042   $173.00   $173.00   $173.00  
  Purchase #5 $205.30   4.242%   $214.0088   $214.01   $214.00   $214.00  
  Purchase #6 $161.95   13.120%   $183.1978   $183.20   $183.20   $183.20  
  Purchase #7 $212.56   13.719%   $241.7211   $241.72   $241.70   $241.70  
  7 purchase totals = $1,135.74       $1,252.1255   $1,252.13   $1,252.10   $1,252.10