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	$38.67	4.278%	$40.3243	$40.32	$40.30	$40.30
Purchase #2	$187.49	11.640%	$209.3138	$209.31	$209.30	$209.30
Purchase #3	$131.84	10.821%	$146.1064	$146.11	$146.10	$146.10
Purchase #4	$88.33	11.329%	$98.3369	$98.34	$98.35	$98.30
Purchase #5	$30.54	6.290%	$32.461	$32.46	$32.45	$32.50
Purchase #6	$176.70	8.322%	$191.405	$191.41	$191.40	$191.40
Purchase #7	$193.39	13.714%	$219.9115	$219.91	$219.90	$219.90
7 purchase totals =	$846.96		$937.8589	$937.86	$937.80	$937.80