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	$93.53	11.553%	$104.3355	$104.34	$104.35	$104.30
Purchase #2	$91.66	5.698%	$96.8828	$96.88	$96.90	$96.90
Purchase #3	$149.41	6.623%	$159.3054	$159.31	$159.30	$159.30
Purchase #4	$7.88	8.622%	$8.5594	$8.56	$8.55	$8.60
Purchase #5	$190.46	7.370%	$204.4969	$204.50	$204.50	$204.50
Purchase #6	$37.53	13.261%	$42.5069	$42.51	$42.50	$42.50
Purchase #7	$180.80	5.613%	$190.9483	$190.95	$190.95	$190.90
7 purchase totals =	$751.27		$807.0352	$807.05	$807.05	$807.00