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 $58.88   8.731%   $64.0208   $64.02   $64.00   $64.00  
  Purchase #2 $212.80   9.317%   $232.6266   $232.63   $232.65   $232.60  
  Purchase #3 $77.91   9.596%   $85.3862   $85.39   $85.40   $85.40  
  Purchase #4 $240.42   5.577%   $253.8282   $253.83   $253.85   $253.80  
  Purchase #5 $101.86   3.306%   $105.2275   $105.23   $105.25   $105.20  
  Purchase #6 $100.64   13.429%   $114.1549   $114.15   $114.15   $114.20  
  Purchase #7 $102.87   6.215%   $109.2634   $109.26   $109.25   $109.30  
  7 purchase totals = $895.38       $964.5076   $964.51   $964.55   $964.50