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 $67.64   13.702%   $76.908   $76.91   $76.90   $76.90  
  Purchase #2 $124.77   6.106%   $132.3885   $132.39   $132.40   $132.40  
  Purchase #3 $178.85   7.145%   $191.6288   $191.63   $191.65   $191.60  
  Purchase #4 $110.45   7.831%   $119.0993   $119.10   $119.10   $119.10  
  Purchase #5 $135.44   4.202%   $141.1312   $141.13   $141.15   $141.10  
  Purchase #6 $59.49   9.415%   $65.091   $65.09   $65.10   $65.10  
  Purchase #7 $236.77   8.121%   $255.9981   $256.00   $256.00   $256.00  
  7 purchase totals = $913.41       $982.2449   $982.25   $982.30   $982.20