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	$136.38	13.497%	$154.7872	$154.79	$154.80	$154.80
Purchase #2	$218.73	11.433%	$243.7374	$243.74	$243.75	$243.70
Purchase #3	$236.45	12.667%	$266.4011	$266.40	$266.40	$266.40
Purchase #4	$127.40	9.179%	$139.094	$139.09	$139.10	$139.10
Purchase #5	$78.38	9.136%	$85.5408	$85.54	$85.55	$85.50
Purchase #6	$27.97	8.369%	$30.3108	$30.31	$30.30	$30.30
Purchase #7	$80.28	3.544%	$83.1251	$83.13	$83.15	$83.10
7 purchase totals =	$905.59		$1,002.9964	$1,003.00	$1,003.05	$1,002.90