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 $61.93   7.590%   $66.6305   $66.63   $66.65   $66.60  
  Purchase #2 $10.64   12.594%   $11.98   $11.98   $12.00   $12.00  
  Purchase #3 $46.80   3.379%   $48.3814   $48.38   $48.40   $48.40  
  Purchase #4 $240.81   9.603%   $263.935   $263.94   $263.95   $263.90  
  Purchase #5 $129.41   11.527%   $144.3271   $144.33   $144.35   $144.30  
  Purchase #6 $163.73   10.592%   $181.0723   $181.07   $181.05   $181.10  
  Purchase #7 $38.27   11.251%   $42.5758   $42.58   $42.60   $42.60  
  7 purchase totals = $691.59       $758.9021   $758.91   $759.00   $758.90