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 $39.28   10.185%   $43.2807   $43.28   $43.30   $43.30  
  Purchase #2 $221.99   4.806%   $232.6588   $232.66   $232.65   $232.70  
  Purchase #3 $118.58   7.439%   $127.4012   $127.40   $127.40   $127.40  
  Purchase #4 $240.52   5.368%   $253.4311   $253.43   $253.45   $253.40  
  Purchase #5 $17.73   12.244%   $19.9009   $19.90   $19.90   $19.90  
  Purchase #6 $28.28   3.152%   $29.1714   $29.17   $29.15   $29.20  
  Purchase #7 $238.95   4.647%   $250.054   $250.05   $250.05   $250.10  
  7 purchase totals = $905.33       $955.8981   $955.89   $955.90   $956.00