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 $217.73   4.328%   $227.1534   $227.15   $227.15   $227.20  
  Purchase #2 $174.83   3.592%   $181.1099   $181.11   $181.10   $181.10  
  Purchase #3 $182.35   10.639%   $201.7502   $201.75   $201.75   $201.80  
  Purchase #4 $242.93   12.792%   $274.0056   $274.01   $274.00   $274.00  
  Purchase #5 $197.70   9.852%   $217.1774   $217.18   $217.20   $217.20  
  Purchase #6 $240.35   8.302%   $260.3039   $260.30   $260.30   $260.30  
  Purchase #7 $218.77   6.117%   $232.1522   $232.15   $232.15   $232.20  
  7 purchase totals = $1,474.66       $1,593.6526   $1,593.65   $1,593.65   $1,593.80