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	$180.66	11.136%	$200.7783	$200.78	$200.80	$200.80
Purchase #2	$12.80	4.780%	$13.4118	$13.41	$13.40	$13.40
Purchase #3	$26.98	7.181%	$28.9174	$28.92	$28.90	$28.90
Purchase #4	$191.93	4.301%	$200.1849	$200.18	$200.20	$200.20
Purchase #5	$55.78	5.587%	$58.8964	$58.90	$58.90	$58.90
Purchase #6	$175.84	7.820%	$189.5907	$189.59	$189.60	$189.60
Purchase #7	$128.95	11.218%	$143.4156	$143.42	$143.40	$143.40
7 purchase totals =	$772.94		$835.1951	$835.20	$835.20	$835.20