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 $224.81   7.287%   $241.1919   $241.19   $241.20   $241.20  
  Purchase #2 $90.85   9.529%   $99.5071   $99.51   $99.50   $99.50  
  Purchase #3 $5.53   9.743%   $6.0688   $6.07   $6.05   $6.10  
  Purchase #4 $77.55   7.752%   $83.5617   $83.56   $83.55   $83.60  
  Purchase #5 $6.71   5.459%   $7.0763   $7.08   $7.10   $7.10  
  Purchase #6 $216.95   9.469%   $237.493   $237.49   $237.50   $237.50  
  Purchase #7 $118.49   7.268%   $127.1019   $127.10   $127.10   $127.10  
  7 purchase totals = $740.89       $802.0007   $802.00   $802.00   $802.10