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 $94.59   10.230%   $104.2666   $104.27   $104.25   $104.30  
  Purchase #2 $223.83   10.746%   $247.8828   $247.88   $247.90   $247.90  
  Purchase #3 $92.93   7.110%   $99.5373   $99.54   $99.55   $99.50  
  Purchase #4 $224.39   5.564%   $236.8751   $236.88   $236.90   $236.90  
  Purchase #5 $51.77   4.163%   $53.9252   $53.93   $53.95   $53.90  
  Purchase #6 $162.59   11.317%   $180.9903   $180.99   $181.00   $181.00  
  Purchase #7 $32.34   11.573%   $36.0827   $36.08   $36.10   $36.10  
  7 purchase totals = $882.44       $959.5600   $959.57   $959.65   $959.60