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	$91.28	13.671%	$103.7589	$103.76	$103.75	$103.80
Purchase #2	$78.47	8.711%	$85.3055	$85.31	$85.30	$85.30
Purchase #3	$237.69	13.578%	$269.9635	$269.96	$269.95	$270.00
Purchase #4	$118.91	10.129%	$130.9544	$130.95	$130.95	$131.00
Purchase #5	$191.74	4.654%	$200.6636	$200.66	$200.65	$200.70
Purchase #6	$218.69	4.327%	$228.1527	$228.15	$228.15	$228.20
Purchase #7	$96.88	8.422%	$105.0392	$105.04	$105.05	$105.00
7 purchase totals =	$1,033.66		$1,123.8378	$1,123.83	$1,123.80	$1,124.00