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	$220.90	3.449%	$228.5188	$228.52	$228.50	$228.50
Purchase #2	$37.48	12.736%	$42.2535	$42.25	$42.25	$42.30
Purchase #3	$88.57	13.387%	$100.4269	$100.43	$100.45	$100.40
Purchase #4	$164.86	11.439%	$183.7183	$183.72	$183.70	$183.70
Purchase #5	$23.59	13.104%	$26.6812	$26.68	$26.70	$26.70
Purchase #6	$36.55	4.778%	$38.2964	$38.30	$38.30	$38.30
Purchase #7	$33.32	7.672%	$35.8763	$35.88	$35.90	$35.90
7 purchase totals =	$605.27		$655.7714	$655.78	$655.80	$655.80