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	$33.62	12.386%	$37.7842	$37.78	$37.80	$37.80
Purchase #2	$31.94	11.636%	$35.6565	$35.66	$35.65	$35.70
Purchase #3	$155.82	10.520%	$172.2123	$172.21	$172.20	$172.20
Purchase #4	$161.64	6.657%	$172.4004	$172.40	$172.40	$172.40
Purchase #5	$182.53	4.511%	$190.7639	$190.76	$190.75	$190.80
Purchase #6	$156.62	13.761%	$178.1725	$178.17	$178.15	$178.20
Purchase #7	$215.98	13.777%	$245.7356	$245.74	$245.75	$245.70
7 purchase totals =	$938.15		$1,032.7254	$1,032.72	$1,032.70	$1,032.80