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	$250.69	5.526%	$264.5431	$264.54	$264.55	$264.50
Purchase #2	$164.28	3.609%	$170.2089	$170.21	$170.20	$170.20
Purchase #3	$74.72	11.263%	$83.1357	$83.14	$83.15	$83.10
Purchase #4	$123.81	5.761%	$130.9427	$130.94	$130.95	$130.90
Purchase #5	$32.48	3.821%	$33.7211	$33.72	$33.70	$33.70
Purchase #6	$147.47	3.590%	$152.7642	$152.76	$152.75	$152.80
Purchase #7	$8.93	7.218%	$9.5746	$9.57	$9.55	$9.60
7 purchase totals =	$802.38		$844.8903	$844.88	$844.85	$844.80