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 $243.33   8.605%   $264.2685   $264.27   $264.25   $264.30  
  Purchase #2 $95.32   7.685%   $102.6453   $102.65   $102.65   $102.60  
  Purchase #3 $13.98   10.319%   $15.4226   $15.42   $15.40   $15.40  
  Purchase #4 $240.91   12.599%   $271.2623   $271.26   $271.25   $271.30  
  Purchase #5 $24.87   7.674%   $26.7785   $26.78   $26.80   $26.80  
  Purchase #6 $59.84   13.796%   $68.0955   $68.10   $68.10   $68.10  
  Purchase #7 $249.26   7.557%   $268.0966   $268.10   $268.10   $268.10  
  7 purchase totals = $927.51       $1,016.5693   $1,016.58   $1,016.55   $1,016.60