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 $34.85   9.356%   $38.1106   $38.11   $38.10   $38.10  
  Purchase #2 $119.98   13.126%   $135.7286   $135.73   $135.75   $135.70  
  Purchase #3 $218.29   9.587%   $239.2175   $239.22   $239.20   $239.20  
  Purchase #4 $199.85   3.317%   $206.479   $206.48   $206.50   $206.50  
  Purchase #5 $204.28   7.807%   $220.2281   $220.23   $220.25   $220.20  
  Purchase #6 $233.35   12.219%   $261.863   $261.86   $261.85   $261.90  
  Purchase #7 $46.95   6.481%   $49.9928   $49.99   $50.00   $50.00  
  7 purchase totals = $1,057.55       $1,151.6196   $1,151.62   $1,151.65   $1,151.60