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	$17.36	4.161%	$18.0823	$18.08	$18.10	$18.10
Purchase #2	$62.62	7.175%	$67.113	$67.11	$67.10	$67.10
Purchase #3	$66.41	8.766%	$72.2315	$72.23	$72.25	$72.20
Purchase #4	$178.43	11.715%	$199.3331	$199.33	$199.35	$199.30
Purchase #5	$50.39	9.114%	$54.9825	$54.98	$55.00	$55.00
Purchase #6	$221.31	9.404%	$242.122	$242.12	$242.10	$242.10
Purchase #7	$235.32	12.205%	$264.0408	$264.04	$264.05	$264.00
7 purchase totals =	$831.84		$917.9052	$917.89	$917.95	$917.80