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	$132.32	3.340%	$136.7395	$136.74	$136.75	$136.70
Purchase #2	$247.78	6.837%	$264.7207	$264.72	$264.70	$264.70
Purchase #3	$181.29	13.251%	$205.3127	$205.31	$205.30	$205.30
Purchase #4	$42.89	4.813%	$44.9543	$44.95	$44.95	$45.00
Purchase #5	$134.79	3.132%	$139.0116	$139.01	$139.00	$139.00
Purchase #6	$154.57	11.457%	$172.2791	$172.28	$172.30	$172.30
Purchase #7	$62.49	7.584%	$67.2292	$67.23	$67.25	$67.20
7 purchase totals =	$956.13		$1,030.2471	$1,030.24	$1,030.25	$1,030.20