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	$41.90	13.369%	$47.5016	$47.50	$47.50	$47.50
Purchase #2	$140.98	10.824%	$156.2397	$156.24	$156.25	$156.20
Purchase #3	$13.78	12.801%	$15.544	$15.54	$15.55	$15.50
Purchase #4	$180.83	13.749%	$205.6923	$205.69	$205.70	$205.70
Purchase #5	$215.47	4.578%	$225.3342	$225.33	$225.35	$225.30
Purchase #6	$37.89	11.732%	$42.3353	$42.34	$42.35	$42.30
Purchase #7	$221.67	9.336%	$242.3651	$242.37	$242.35	$242.40
7 purchase totals =	$852.52		$935.0122	$935.01	$935.05	$934.90