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	$95.80	8.283%	$103.7351	$103.74	$103.75	$103.70
Purchase #2	$80.71	12.809%	$91.0481	$91.05	$91.05	$91.00
Purchase #3	$221.27	11.633%	$247.0103	$247.01	$247.00	$247.00
Purchase #4	$130.92	11.648%	$146.1696	$146.17	$146.15	$146.20
Purchase #5	$73.46	7.142%	$78.7065	$78.71	$78.70	$78.70
Purchase #6	$231.91	6.628%	$247.281	$247.28	$247.30	$247.30
Purchase #7	$60.76	6.684%	$64.8212	$64.82	$64.80	$64.80
7 purchase totals =	$894.83		$978.7718	$978.78	$978.75	$978.70