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	$99.60	11.676%	$111.2293	$111.23	$111.25	$111.20
Purchase #2	$50.85	9.762%	$55.814	$55.81	$55.80	$55.80
Purchase #3	$80.64	6.501%	$85.8824	$85.88	$85.90	$85.90
Purchase #4	$37.56	13.374%	$42.5833	$42.58	$42.60	$42.60
Purchase #5	$151.71	13.185%	$171.713	$171.71	$171.70	$171.70
Purchase #6	$151.28	11.245%	$168.2914	$168.29	$168.30	$168.30
Purchase #7	$226.66	9.844%	$248.9724	$248.97	$248.95	$249.00
7 purchase totals =	$798.30		$884.4858	$884.47	$884.50	$884.50