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 $83.87   10.588%   $92.7502   $92.75   $92.75   $92.80  
  Purchase #2 $131.87   3.303%   $136.2257   $136.23   $136.25   $136.20  
  Purchase #3 $41.36   7.574%   $44.4926   $44.49   $44.50   $44.50  
  Purchase #4 $194.75   5.527%   $205.5138   $205.51   $205.50   $205.50  
  Purchase #5 $80.67   7.482%   $86.7057   $86.71   $86.70   $86.70  
  Purchase #6 $220.28   7.489%   $236.7768   $236.78   $236.80   $236.80  
  Purchase #7 $140.85   3.806%   $146.2108   $146.21   $146.20   $146.20  
  7 purchase totals = $893.65       $948.6756   $948.68   $948.70   $948.70