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	$98.66	12.585%	$111.0764	$111.08	$111.10	$111.10
Purchase #2	$217.69	12.815%	$245.587	$245.59	$245.60	$245.60
Purchase #3	$25.35	13.207%	$28.698	$28.70	$28.70	$28.70
Purchase #4	$101.51	7.579%	$109.2034	$109.20	$109.20	$109.20
Purchase #5	$238.87	3.127%	$246.3395	$246.34	$246.35	$246.30
Purchase #6	$80.51	12.571%	$90.6309	$90.63	$90.65	$90.60
Purchase #7	$153.74	7.368%	$165.0676	$165.07	$165.05	$165.10
7 purchase totals =	$916.33		$996.6028	$996.61	$996.65	$996.60