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	$60.71	13.682%	$69.0163	$69.02	$69.00	$69.00
Purchase #2	$197.31	3.246%	$203.7147	$203.71	$203.70	$203.70
Purchase #3	$35.69	13.245%	$40.4171	$40.42	$40.40	$40.40
Purchase #4	$227.71	9.199%	$248.657	$248.66	$248.65	$248.70
Purchase #5	$122.74	6.860%	$131.16	$131.16	$131.15	$131.20
Purchase #6	$127.87	11.738%	$142.8794	$142.88	$142.90	$142.90
Purchase #7	$248.27	6.571%	$264.5838	$264.58	$264.60	$264.60
7 purchase totals =	$1,020.30		$1,100.4283	$1,100.43	$1,100.40	$1,100.50