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 $88.30   7.166%   $94.6276   $94.63   $94.65   $94.60  
  Purchase #2 $226.93   3.598%   $235.0949   $235.09   $235.10   $235.10  
  Purchase #3 $103.55   6.130%   $109.8976   $109.90   $109.90   $109.90  
  Purchase #4 $223.49   9.849%   $245.5015   $245.50   $245.50   $245.50  
  Purchase #5 $106.29   11.490%   $118.5027   $118.50   $118.50   $118.50  
  Purchase #6 $7.65   6.823%   $8.172   $8.17   $8.15   $8.20  
  Purchase #7 $25.75   5.814%   $27.2471   $27.25   $27.25   $27.20  
  7 purchase totals = $781.96       $839.0434   $839.04   $839.05   $839.00