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	$189.33	5.226%	$199.2244	$199.22	$199.20	$199.20
Purchase #2	$115.63	9.655%	$126.7941	$126.79	$126.80	$126.80
Purchase #3	$111.93	10.238%	$123.3894	$123.39	$123.40	$123.40
Purchase #4	$216.37	13.567%	$245.7249	$245.72	$245.70	$245.70
Purchase #5	$79.51	4.708%	$83.2533	$83.25	$83.25	$83.30
Purchase #6	$55.57	7.808%	$59.9089	$59.91	$59.90	$59.90
Purchase #7	$149.29	3.870%	$155.0675	$155.07	$155.05	$155.10
7 purchase totals =	$917.63		$993.3625	$993.35	$993.30	$993.40