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	$74.89	10.500%	$82.7535	$82.75	$82.75	$82.80
Purchase #2	$160.88	13.568%	$182.7082	$182.71	$182.70	$182.70
Purchase #3	$58.33	11.513%	$65.0455	$65.05	$65.05	$65.00
Purchase #4	$31.97	10.225%	$35.2389	$35.24	$35.25	$35.20
Purchase #5	$113.33	4.680%	$118.6338	$118.63	$118.65	$118.60
Purchase #6	$205.34	8.634%	$223.0691	$223.07	$223.05	$223.10
Purchase #7	$78.39	9.641%	$85.9476	$85.95	$85.95	$85.90
7 purchase totals =	$723.13		$793.3966	$793.40	$793.40	$793.30