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	$180.71	11.170%	$200.8953	$200.90	$200.90	$200.90
Purchase #2	$108.28	4.163%	$112.7877	$112.79	$112.80	$112.80
Purchase #3	$184.54	8.225%	$199.7184	$199.72	$199.70	$199.70
Purchase #4	$147.69	4.221%	$153.924	$153.92	$153.90	$153.90
Purchase #5	$67.61	13.143%	$76.496	$76.50	$76.50	$76.50
Purchase #6	$52.34	11.278%	$58.2429	$58.24	$58.25	$58.20
Purchase #7	$19.64	4.263%	$20.4773	$20.48	$20.50	$20.50
7 purchase totals =	$760.81		$822.5416	$822.55	$822.55	$822.50