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	$124.43	9.801%	$136.6254	$136.63	$136.65	$136.60
Purchase #2	$205.81	7.815%	$221.8941	$221.89	$221.90	$221.90
Purchase #3	$26.90	5.742%	$28.4446	$28.44	$28.45	$28.40
Purchase #4	$238.48	12.817%	$269.046	$269.05	$269.05	$269.00
Purchase #5	$145.80	13.707%	$165.7848	$165.78	$165.80	$165.80
Purchase #6	$227.48	10.434%	$251.2153	$251.22	$251.20	$251.20
Purchase #7	$56.94	4.202%	$59.3326	$59.33	$59.35	$59.30
7 purchase totals =	$1,025.84		$1,132.3428	$1,132.34	$1,132.40	$1,132.20