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	$131.60	6.191%	$139.7474	$139.75	$139.75	$139.70
Purchase #2	$34.46	7.843%	$37.1627	$37.16	$37.15	$37.20
Purchase #3	$152.39	11.265%	$169.5567	$169.56	$169.55	$169.60
Purchase #4	$232.64	5.544%	$245.5376	$245.54	$245.55	$245.50
Purchase #5	$47.33	9.676%	$51.9097	$51.91	$51.90	$51.90
Purchase #6	$88.82	12.178%	$99.6365	$99.64	$99.65	$99.60
Purchase #7	$153.46	11.353%	$170.8823	$170.88	$170.90	$170.90
7 purchase totals =	$840.70		$914.4329	$914.44	$914.45	$914.40