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 $19.50   6.845%   $20.8348   $20.83   $20.85   $20.80  
  Purchase #2 $199.27   3.209%   $205.6646   $205.66   $205.65   $205.70  
  Purchase #3 $115.86   10.779%   $128.3485   $128.35   $128.35   $128.30  
  Purchase #4 $97.59   13.400%   $110.6671   $110.67   $110.65   $110.70  
  Purchase #5 $49.25   3.700%   $51.0723   $51.07   $51.05   $51.10  
  Purchase #6 $230.70   7.180%   $247.2643   $247.26   $247.25   $247.30  
  Purchase #7 $108.49   7.258%   $116.3642   $116.36   $116.35   $116.40  
  7 purchase totals = $820.66       $880.2158   $880.20   $880.15   $880.30