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	$48.38	7.178%	$51.8527	$51.85	$51.85	$51.90
Purchase #2	$80.61	11.645%	$89.997	$90.00	$90.00	$90.00
Purchase #3	$165.84	11.769%	$185.3577	$185.36	$185.35	$185.40
Purchase #4	$80.31	11.175%	$89.2846	$89.28	$89.30	$89.30
Purchase #5	$123.53	5.146%	$129.8869	$129.89	$129.90	$129.90
Purchase #6	$191.60	4.669%	$200.5458	$200.55	$200.55	$200.50
Purchase #7	$81.73	8.370%	$88.5708	$88.57	$88.55	$88.60
7 purchase totals =	$772.00		$835.4955	$835.50	$835.50	$835.60