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	$114.88	12.111%	$128.7931	$128.79	$128.80	$128.80
Purchase #2	$171.73	9.504%	$188.0512	$188.05	$188.05	$188.10
Purchase #3	$91.45	9.621%	$100.2484	$100.25	$100.25	$100.20
Purchase #4	$153.76	11.639%	$171.6561	$171.66	$171.65	$171.70
Purchase #5	$60.49	7.173%	$64.8289	$64.83	$64.85	$64.80
Purchase #6	$126.89	8.307%	$137.4308	$137.43	$137.45	$137.40
Purchase #7	$186.33	12.402%	$209.4386	$209.44	$209.45	$209.40
7 purchase totals =	$905.53		$1,000.4471	$1,000.45	$1,000.50	$1,000.40