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 $14.87   4.392%   $15.5231   $15.52   $15.50   $15.50  
  Purchase #2 $238.64   12.284%   $267.9545   $267.95   $267.95   $268.00  
  Purchase #3 $54.35   8.298%   $58.86   $58.86   $58.85   $58.90  
  Purchase #4 $171.66   6.492%   $182.8042   $182.80   $182.80   $182.80  
  Purchase #5 $6.50   12.855%   $7.3356   $7.34   $7.35   $7.30  
  Purchase #6 $180.83   8.747%   $196.6472   $196.65   $196.65   $196.60  
  Purchase #7 $217.51   9.109%   $237.323   $237.32   $237.30   $237.30  
  7 purchase totals = $884.36       $966.4476   $966.44   $966.40   $966.40