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	$146.33	13.364%	$165.8855	$165.89	$165.90	$165.90
Purchase #2	$105.83	11.112%	$117.5898	$117.59	$117.60	$117.60
Purchase #3	$134.28	13.235%	$152.052	$152.05	$152.05	$152.10
Purchase #4	$91.90	11.577%	$102.5393	$102.54	$102.55	$102.50
Purchase #5	$125.90	11.787%	$140.7398	$140.74	$140.75	$140.70
Purchase #6	$130.50	6.265%	$138.6758	$138.68	$138.70	$138.70
Purchase #7	$68.86	6.585%	$73.3944	$73.39	$73.40	$73.40
7 purchase totals =	$803.60		$890.8766	$890.88	$890.95	$890.90