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	13.239%	$83.5477	$83.55	$83.55	$83.50
Purchase #2	$31.90	10.369%	$35.2077	$35.21	$35.20	$35.20
Purchase #3	$162.36	10.384%	$179.2195	$179.22	$179.20	$179.20
Purchase #4	$246.48	11.308%	$274.352	$274.35	$274.35	$274.40
Purchase #5	$144.29	5.829%	$152.7007	$152.70	$152.70	$152.70
Purchase #6	$239.51	5.669%	$253.0878	$253.09	$253.10	$253.10
Purchase #7	$108.83	4.211%	$113.4128	$113.41	$113.40	$113.40
7 purchase totals =	$1,007.15		$1,091.5282	$1,091.53	$1,091.50	$1,091.50