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	$86.53	3.819%	$89.8346	$89.83	$89.85	$89.80
Purchase #2	$235.32	4.485%	$245.8741	$245.87	$245.85	$245.90
Purchase #3	$100.93	10.152%	$111.1764	$111.18	$111.20	$111.20
Purchase #4	$20.68	9.140%	$22.5702	$22.57	$22.55	$22.60
Purchase #5	$242.57	12.543%	$272.9956	$273.00	$273.00	$273.00
Purchase #6	$30.34	9.223%	$33.1383	$33.14	$33.15	$33.10
Purchase #7	$128.96	4.280%	$134.4795	$134.48	$134.50	$134.50
7 purchase totals =	$845.33		$910.0687	$910.07	$910.10	$910.10