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 $201.29   4.133%   $209.6093   $209.61   $209.60   $209.60  
  Purchase #2 $83.44   4.849%   $87.486   $87.49   $87.50   $87.50  
  Purchase #3 $23.69   9.618%   $25.9685   $25.97   $25.95   $26.00  
  Purchase #4 $176.95   8.326%   $191.6829   $191.68   $191.70   $191.70  
  Purchase #5 $212.85   5.497%   $224.5504   $224.55   $224.55   $224.60  
  Purchase #6 $140.67   12.763%   $158.6237   $158.62   $158.60   $158.60  
  Purchase #7 $25.75   13.794%   $29.302   $29.30   $29.30   $29.30  
  7 purchase totals = $864.64       $927.2228   $927.22   $927.20   $927.30