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	$77.80	9.464%	$85.163	$85.16	$85.15	$85.20
Purchase #2	$161.49	4.178%	$168.2371	$168.24	$168.25	$168.20
Purchase #3	$134.49	8.117%	$145.4066	$145.41	$145.40	$145.40
Purchase #4	$20.89	6.366%	$22.2199	$22.22	$22.20	$22.20
Purchase #5	$245.70	10.113%	$270.5476	$270.55	$270.55	$270.50
Purchase #6	$129.50	9.770%	$142.1522	$142.15	$142.15	$142.20
Purchase #7	$223.30	12.133%	$250.393	$250.39	$250.40	$250.40
7 purchase totals =	$993.17		$1,084.1194	$1,084.12	$1,084.10	$1,084.10