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 $53.85   11.786%   $60.1968   $60.20   $60.20   $60.20  
  Purchase #2 $193.31   12.741%   $217.9396   $217.94   $217.95   $217.90  
  Purchase #3 $171.25   13.251%   $193.9423   $193.94   $193.95   $193.90  
  Purchase #4 $5.69   12.241%   $6.3865   $6.39   $6.40   $6.40  
  Purchase #5 $239.84   5.440%   $252.8873   $252.89   $252.90   $252.90  
  Purchase #6 $100.90   8.228%   $109.2021   $109.20   $109.20   $109.20  
  Purchase #7 $50.71   8.367%   $54.9529   $54.95   $54.95   $55.00  
  7 purchase totals = $815.55       $895.5075   $895.51   $895.55   $895.50