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	$140.58	5.478%	$148.281	$148.28	$148.30	$148.30
Purchase #2	$36.26	3.170%	$37.4094	$37.41	$37.40	$37.40
Purchase #3	$188.85	4.225%	$196.8289	$196.83	$196.85	$196.80
Purchase #4	$157.56	11.601%	$175.8385	$175.84	$175.85	$175.80
Purchase #5	$150.83	7.382%	$161.9643	$161.96	$161.95	$162.00
Purchase #6	$40.95	12.181%	$45.9381	$45.94	$45.95	$45.90
Purchase #7	$35.85	11.191%	$39.862	$39.86	$39.85	$39.90
7 purchase totals =	$750.88		$806.1222	$806.12	$806.15	$806.10