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	$15.32	13.196%	$17.3416	$17.34	$17.35	$17.30
Purchase #2	$242.53	10.592%	$268.2188	$268.22	$268.20	$268.20
Purchase #3	$81.41	9.452%	$89.1049	$89.10	$89.10	$89.10
Purchase #4	$93.71	11.452%	$104.4417	$104.44	$104.45	$104.40
Purchase #5	$244.68	13.571%	$277.8855	$277.89	$277.90	$277.90
Purchase #6	$90.53	10.853%	$100.3552	$100.36	$100.35	$100.40
Purchase #7	$221.70	8.790%	$241.1874	$241.19	$241.20	$241.20
7 purchase totals =	$989.88		$1,098.5351	$1,098.54	$1,098.55	$1,098.50