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	$127.88	13.325%	$144.92	$144.92	$144.90	$144.90
Purchase #2	$160.58	11.125%	$178.4445	$178.44	$178.45	$178.40
Purchase #3	$40.56	11.862%	$45.3712	$45.37	$45.35	$45.40
Purchase #4	$125.35	13.401%	$142.1482	$142.15	$142.15	$142.10
Purchase #5	$234.91	11.294%	$261.4407	$261.44	$261.45	$261.40
Purchase #6	$16.61	6.121%	$17.6267	$17.63	$17.65	$17.60
Purchase #7	$212.66	7.111%	$227.7823	$227.78	$227.80	$227.80
7 purchase totals =	$918.55		$1,017.7336	$1,017.73	$1,017.75	$1,017.60