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	$81.90	4.140%	$85.2907	$85.29	$85.30	$85.30
Purchase #2	$194.51	10.823%	$215.5618	$215.56	$215.55	$215.60
Purchase #3	$138.27	6.740%	$147.5894	$147.59	$147.60	$147.60
Purchase #4	$93.92	10.371%	$103.6604	$103.66	$103.65	$103.70
Purchase #5	$88.99	11.190%	$98.948	$98.95	$98.95	$98.90
Purchase #6	$242.70	9.555%	$265.89	$265.89	$265.90	$265.90
Purchase #7	$152.67	8.138%	$165.0943	$165.09	$165.10	$165.10
7 purchase totals =	$992.96		$1,082.0346	$1,082.03	$1,082.05	$1,082.10