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	$179.93	10.825%	$199.4074	$199.41	$199.40	$199.40
Purchase #2	$247.89	12.527%	$278.9432	$278.94	$278.95	$278.90
Purchase #3	$88.32	12.250%	$99.1392	$99.14	$99.15	$99.10
Purchase #4	$151.48	3.854%	$157.318	$157.32	$157.30	$157.30
Purchase #5	$220.70	4.135%	$229.8259	$229.83	$229.85	$229.80
Purchase #6	$59.76	13.528%	$67.8443	$67.84	$67.85	$67.80
Purchase #7	$77.31	12.319%	$86.8338	$86.83	$86.85	$86.80
7 purchase totals =	$1,025.39		$1,119.3118	$1,119.31	$1,119.35	$1,119.10