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	$34.29	8.840%	$37.3212	$37.32	$37.30	$37.30
Purchase #2	$179.86	9.205%	$196.4161	$196.42	$196.40	$196.40
Purchase #3	$220.39	11.268%	$245.2235	$245.22	$245.20	$245.20
Purchase #4	$83.28	3.157%	$85.9091	$85.91	$85.90	$85.90
Purchase #5	$147.34	13.561%	$167.3208	$167.32	$167.30	$167.30
Purchase #6	$161.46	8.867%	$175.7767	$175.78	$175.80	$175.80
Purchase #7	$95.43	4.278%	$99.5125	$99.51	$99.50	$99.50
7 purchase totals =	$922.05		$1,007.4799	$1,007.48	$1,007.40	$1,007.40