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 $208.29   8.289%   $225.5552   $225.56   $225.55   $225.60  
  Purchase #2 $41.32   13.583%   $46.9325   $46.93   $46.95   $46.90  
  Purchase #3 $243.25   4.496%   $254.1865   $254.19   $254.20   $254.20  
  Purchase #4 $50.27   12.853%   $56.7312   $56.73   $56.75   $56.70  
  Purchase #5 $94.50   13.618%   $107.369   $107.37   $107.35   $107.40  
  Purchase #6 $11.36   13.149%   $12.8537   $12.85   $12.85   $12.90  
  Purchase #7 $21.45   12.362%   $24.1016   $24.10   $24.10   $24.10  
  7 purchase totals = $670.44       $727.7297   $727.73   $727.75   $727.80