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	$73.78	10.746%	$81.7084	$81.71	$81.70	$81.70
Purchase #2	$72.34	8.504%	$78.4918	$78.49	$78.50	$78.50
Purchase #3	$154.36	8.860%	$168.0363	$168.04	$168.05	$168.00
Purchase #4	$142.89	7.558%	$153.6896	$153.69	$153.70	$153.70
Purchase #5	$184.51	11.708%	$206.1124	$206.11	$206.10	$206.10
Purchase #6	$172.80	10.804%	$191.4693	$191.47	$191.45	$191.50
Purchase #7	$35.96	3.580%	$37.2474	$37.25	$37.25	$37.20
7 purchase totals =	$836.64		$916.7552	$916.76	$916.75	$916.70