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	$198.81	12.658%	$223.9754	$223.98	$224.00	$224.00
Purchase #2	$35.70	4.731%	$37.389	$37.39	$37.40	$37.40
Purchase #3	$123.80	12.723%	$139.5511	$139.55	$139.55	$139.60
Purchase #4	$89.51	8.541%	$97.155	$97.16	$97.15	$97.20
Purchase #5	$91.50	8.245%	$99.0442	$99.04	$99.05	$99.00
Purchase #6	$148.86	13.463%	$168.901	$168.90	$168.90	$168.90
Purchase #7	$78.81	13.753%	$89.6487	$89.65	$89.65	$89.60
7 purchase totals =	$766.99		$855.6644	$855.67	$855.70	$855.70