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 $61.91   9.783%   $67.9667   $67.97   $67.95   $68.00  
  Purchase #2 $165.68   11.255%   $184.3273   $184.33   $184.35   $184.30  
  Purchase #3 $204.55   3.480%   $211.6683   $211.67   $211.65   $211.70  
  Purchase #4 $203.75   4.785%   $213.4994   $213.50   $213.50   $213.50  
  Purchase #5 $47.72   13.446%   $54.1364   $54.14   $54.15   $54.10  
  Purchase #6 $82.32   12.196%   $92.3597   $92.36   $92.35   $92.40  
  Purchase #7 $151.44   7.187%   $162.324   $162.32   $162.30   $162.30  
  7 purchase totals = $917.37       $986.2818   $986.29   $986.25   $986.30