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	$89.99	12.670%	$101.3917	$101.39	$101.40	$101.40
Purchase #2	$131.94	5.387%	$139.0476	$139.05	$139.05	$139.00
Purchase #3	$93.49	7.767%	$100.7514	$100.75	$100.75	$100.80
Purchase #4	$162.52	10.438%	$179.4838	$179.48	$179.50	$179.50
Purchase #5	$83.69	9.501%	$91.6414	$91.64	$91.65	$91.60
Purchase #6	$184.66	7.165%	$197.8909	$197.89	$197.90	$197.90
Purchase #7	$42.76	6.554%	$45.5625	$45.56	$45.55	$45.60
7 purchase totals =	$789.05		$855.7693	$855.76	$855.80	$855.80