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	$175.73	8.632%	$190.899	$190.90	$190.90	$190.90
Purchase #2	$112.31	9.422%	$122.8918	$122.89	$122.90	$122.90
Purchase #3	$76.89	11.726%	$85.9061	$85.91	$85.90	$85.90
Purchase #4	$162.58	13.822%	$185.0518	$185.05	$185.05	$185.10
Purchase #5	$109.32	7.466%	$117.4818	$117.48	$117.50	$117.50
Purchase #6	$44.98	11.827%	$50.2998	$50.30	$50.30	$50.30
Purchase #7	$7.99	4.616%	$8.3588	$8.36	$8.35	$8.40
7 purchase totals =	$689.80		$760.8891	$760.89	$760.90	$761.00