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 $234.94   12.185%   $263.5674   $263.57   $263.55   $263.60  
  Purchase #2 $119.63   5.719%   $126.4716   $126.47   $126.45   $126.50  
  Purchase #3 $44.74   4.461%   $46.7359   $46.74   $46.75   $46.70  
  Purchase #4 $153.84   6.399%   $163.6842   $163.68   $163.70   $163.70  
  Purchase #5 $213.44   11.733%   $238.4829   $238.48   $238.50   $238.50  
  Purchase #6 $84.25   5.835%   $89.166   $89.17   $89.15   $89.20  
  Purchase #7 $206.38   9.560%   $226.1099   $226.11   $226.10   $226.10  
  7 purchase totals = $1,057.22       $1,154.2179   $1,154.22   $1,154.20   $1,154.30