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 $230.42   8.508%   $250.0241   $250.02   $250.00   $250.00  
  Purchase #2 $246.65   6.613%   $262.961   $262.96   $262.95   $263.00  
  Purchase #3 $20.70   11.392%   $23.0581   $23.06   $23.05   $23.10  
  Purchase #4 $210.34   8.350%   $227.9034   $227.90   $227.90   $227.90  
  Purchase #5 $52.69   9.742%   $57.8231   $57.82   $57.80   $57.80  
  Purchase #6 $189.69   13.117%   $214.5716   $214.57   $214.55   $214.60  
  Purchase #7 $244.79   6.196%   $259.9572   $259.96   $259.95   $260.00  
  7 purchase totals = $1,195.28       $1,296.2985   $1,296.29   $1,296.20   $1,296.40