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	$23.74	13.632%	$26.9762	$26.98	$27.00	$27.00
Purchase #2	$109.34	7.300%	$117.3218	$117.32	$117.30	$117.30
Purchase #3	$29.46	5.778%	$31.1622	$31.16	$31.15	$31.20
Purchase #4	$221.71	6.403%	$235.9061	$235.91	$235.90	$235.90
Purchase #5	$98.73	13.361%	$111.9213	$111.92	$111.90	$111.90
Purchase #6	$196.65	13.766%	$223.7208	$223.72	$223.70	$223.70
Purchase #7	$78.65	12.209%	$88.2524	$88.25	$88.25	$88.30
7 purchase totals =	$758.28		$835.2608	$835.26	$835.20	$835.30