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 $87.50   6.206%   $92.9303   $92.93   $92.95   $92.90  
  Purchase #2 $218.25   5.499%   $230.2516   $230.25   $230.25   $230.30  
  Purchase #3 $104.75   7.116%   $112.204   $112.20   $112.20   $112.20  
  Purchase #4 $48.81   6.802%   $52.1301   $52.13   $52.15   $52.10  
  Purchase #5 $70.35   10.522%   $77.7522   $77.75   $77.75   $77.80  
  Purchase #6 $230.72   11.174%   $256.5007   $256.50   $256.50   $256.50  
  Purchase #7 $31.95   13.387%   $36.2271   $36.23   $36.25   $36.20  
  7 purchase totals = $792.33       $857.9960   $857.99   $858.05   $858.00