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 $229.69   10.535%   $253.8878   $253.89   $253.90   $253.90  
  Purchase #2 $82.30   12.381%   $92.4896   $92.49   $92.50   $92.50  
  Purchase #3 $43.50   10.322%   $47.9901   $47.99   $48.00   $48.00  
  Purchase #4 $232.25   13.550%   $263.7199   $263.72   $263.70   $263.70  
  Purchase #5 $196.71   12.160%   $220.6299   $220.63   $220.65   $220.60  
  Purchase #6 $236.53   9.537%   $259.0879   $259.09   $259.10   $259.10  
  Purchase #7 $211.43   7.117%   $226.4775   $226.48   $226.50   $226.50  
  7 purchase totals = $1,232.41       $1,364.2827   $1,364.29   $1,364.35   $1,364.30