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 $91.85   6.333%   $97.6669   $97.67   $97.65   $97.70  
  Purchase #2 $209.88   11.612%   $234.2513   $234.25   $234.25   $234.30  
  Purchase #3 $236.36   6.731%   $252.2694   $252.27   $252.25   $252.30  
  Purchase #4 $88.61   4.293%   $92.414   $92.41   $92.40   $92.40  
  Purchase #5 $205.60   12.723%   $231.7585   $231.76   $231.75   $231.80  
  Purchase #6 $18.49   5.761%   $19.5552   $19.56   $19.55   $19.60  
  Purchase #7 $85.32   8.181%   $92.3   $92.30   $92.30   $92.30  
  7 purchase totals = $936.11       $1,020.2153   $1,020.22   $1,020.15   $1,020.40