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 $58.97   10.269%   $65.0256   $65.03   $65.05   $65.00  
  Purchase #2 $140.94   5.225%   $148.3041   $148.30   $148.30   $148.30  
  Purchase #3 $20.94   12.137%   $23.4815   $23.48   $23.50   $23.50  
  Purchase #4 $52.65   11.558%   $58.7353   $58.74   $58.75   $58.70  
  Purchase #5 $7.49   12.762%   $8.4459   $8.45   $8.45   $8.40  
  Purchase #6 $110.65   4.627%   $115.7698   $115.77   $115.75   $115.80  
  Purchase #7 $184.94   6.590%   $197.1275   $197.13   $197.15   $197.10  
  7 purchase totals = $576.58       $616.8897   $616.90   $616.95   $616.80