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	$180.69	6.815%	$193.004	$193.00	$193.00	$193.00
Purchase #2	$215.50	11.515%	$240.3148	$240.31	$240.30	$240.30
Purchase #3	$39.45	12.830%	$44.5114	$44.51	$44.50	$44.50
Purchase #4	$118.74	10.644%	$131.3787	$131.38	$131.40	$131.40
Purchase #5	$35.65	12.476%	$40.0977	$40.10	$40.10	$40.10
Purchase #6	$96.29	4.432%	$100.5576	$100.56	$100.55	$100.60
Purchase #7	$56.63	6.473%	$60.2957	$60.30	$60.30	$60.30
7 purchase totals =	$742.95		$810.1599	$810.16	$810.15	$810.20