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 $37.45   13.381%   $42.4612   $42.46   $42.45   $42.50  
  Purchase #2 $242.97   9.314%   $265.6002   $265.60   $265.60   $265.60  
  Purchase #3 $69.60   4.282%   $72.5803   $72.58   $72.60   $72.60  
  Purchase #4 $217.33   13.267%   $246.1632   $246.16   $246.15   $246.20  
  Purchase #5 $189.77   4.864%   $199.0004   $199.00   $199.00   $199.00  
  Purchase #6 $241.64   6.697%   $257.8226   $257.82   $257.80   $257.80  
  Purchase #7 $155.70   9.219%   $170.054   $170.05   $170.05   $170.10  
  7 purchase totals = $1,154.46       $1,253.6819   $1,253.67   $1,253.65   $1,253.80