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 $53.61   11.457%   $59.7521   $59.75   $59.75   $59.80  
  Purchase #2 $92.43   6.401%   $98.3464   $98.35   $98.35   $98.30  
  Purchase #3 $65.32   7.476%   $70.2033   $70.20   $70.20   $70.20  
  Purchase #4 $193.73   9.215%   $211.5822   $211.58   $211.60   $211.60  
  Purchase #5 $41.70   10.174%   $45.9426   $45.94   $45.95   $45.90  
  Purchase #6 $237.73   9.461%   $260.2216   $260.22   $260.20   $260.20  
  Purchase #7 $61.38   10.104%   $67.5818   $67.58   $67.60   $67.60  
  7 purchase totals = $745.90       $813.6300   $813.62   $813.65   $813.60