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 $87.41   12.398%   $98.2471   $98.25   $98.25   $98.20  
  Purchase #2 $127.56   6.634%   $136.0223   $136.02   $136.00   $136.00  
  Purchase #3 $123.52   9.858%   $135.6966   $135.70   $135.70   $135.70  
  Purchase #4 $5.71   6.194%   $6.0637   $6.06   $6.05   $6.10  
  Purchase #5 $221.78   11.149%   $246.5063   $246.51   $246.50   $246.50  
  Purchase #6 $191.66   5.663%   $202.5137   $202.51   $202.50   $202.50  
  Purchase #7 $18.32   5.518%   $19.3309   $19.33   $19.35   $19.30  
  7 purchase totals = $775.96       $844.3806   $844.38   $844.35   $844.30