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 $89.92   9.193%   $98.1863   $98.19   $98.20   $98.20  
  Purchase #2 $168.42   3.265%   $173.9189   $173.92   $173.90   $173.90  
  Purchase #3 $112.99   10.315%   $124.6449   $124.64   $124.65   $124.60  
  Purchase #4 $226.35   4.841%   $237.3076   $237.31   $237.30   $237.30  
  Purchase #5 $60.47   8.152%   $65.3995   $65.40   $65.40   $65.40  
  Purchase #6 $50.72   3.412%   $52.4506   $52.45   $52.45   $52.50  
  Purchase #7 $230.77   6.367%   $245.4631   $245.46   $245.45   $245.50  
  7 purchase totals = $939.64       $997.3709   $997.37   $997.35   $997.40