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 $233.62   9.316%   $255.384   $255.38   $255.40   $255.40  
  Purchase #2 $162.74   6.622%   $173.5166   $173.52   $173.50   $173.50  
  Purchase #3 $73.69   3.398%   $76.194   $76.19   $76.20   $76.20  
  Purchase #4 $147.67   4.838%   $154.8143   $154.81   $154.80   $154.80  
  Purchase #5 $108.80   11.326%   $121.1227   $121.12   $121.10   $121.10  
  Purchase #6 $167.29   11.762%   $186.9666   $186.97   $186.95   $187.00  
  Purchase #7 $52.80   11.720%   $58.9882   $58.99   $59.00   $59.00  
  7 purchase totals = $946.61       $1,026.9864   $1,026.98   $1,026.95   $1,027.00