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 $53.37   5.378%   $56.2402   $56.24   $56.25   $56.20  
  Purchase #2 $195.43   5.823%   $206.8099   $206.81   $206.80   $206.80  
  Purchase #3 $86.51   6.807%   $92.3987   $92.40   $92.40   $92.40  
  Purchase #4 $85.61   4.625%   $89.5695   $89.57   $89.55   $89.60  
  Purchase #5 $37.36   9.396%   $40.8703   $40.87   $40.85   $40.90  
  Purchase #6 $220.38   11.176%   $245.0097   $245.01   $245.00   $245.00  
  Purchase #7 $187.87   6.289%   $199.6851   $199.69   $199.70   $199.70  
  7 purchase totals = $866.53       $930.5834   $930.59   $930.55   $930.60