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	$178.69	6.614%	$190.5086	$190.51	$190.50	$190.50
Purchase #2	$60.44	9.560%	$66.2181	$66.22	$66.20	$66.20
Purchase #3	$228.80	9.550%	$250.6504	$250.65	$250.65	$250.70
Purchase #4	$71.38	9.602%	$78.2339	$78.23	$78.25	$78.20
Purchase #5	$16.89	7.512%	$18.1588	$18.16	$18.15	$18.20
Purchase #6	$57.81	3.121%	$59.6143	$59.61	$59.60	$59.60
Purchase #7	$101.55	6.826%	$108.4818	$108.48	$108.50	$108.50
7 purchase totals =	$715.56		$771.8659	$771.86	$771.85	$771.90