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 $214.32   12.498%   $241.1057   $241.11   $241.10   $241.10  
  Purchase #2 $54.39   6.330%   $57.8329   $57.83   $57.85   $57.80  
  Purchase #3 $246.25   4.380%   $257.0358   $257.04   $257.05   $257.00  
  Purchase #4 $22.55   9.571%   $24.7083   $24.71   $24.70   $24.70  
  Purchase #5 $186.28   4.139%   $193.9901   $193.99   $194.00   $194.00  
  Purchase #6 $55.98   7.620%   $60.2457   $60.25   $60.25   $60.20  
  Purchase #7 $125.88   12.697%   $141.863   $141.86   $141.85   $141.90  
  7 purchase totals = $905.65       $976.7815   $976.79   $976.80   $976.70