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 $151.48   8.261%   $163.9938   $163.99   $164.00   $164.00  
  Purchase #2 $229.92   13.366%   $260.6511   $260.65   $260.65   $260.70  
  Purchase #3 $249.35   10.397%   $275.2749   $275.27   $275.25   $275.30  
  Purchase #4 $236.49   13.654%   $268.7803   $268.78   $268.80   $268.80  
  Purchase #5 $84.77   8.767%   $92.2018   $92.20   $92.20   $92.20  
  Purchase #6 $32.33   5.234%   $34.0222   $34.02   $34.00   $34.00  
  Purchase #7 $29.27   8.271%   $31.6909   $31.69   $31.70   $31.70  
  7 purchase totals = $1,013.61       $1,126.6150   $1,126.60   $1,126.60   $1,126.70