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	$155.73	10.858%	$172.6392	$172.64	$172.65	$172.60
Purchase #2	$44.72	12.668%	$50.3851	$50.39	$50.40	$50.40
Purchase #3	$145.65	7.202%	$156.1397	$156.14	$156.15	$156.10
Purchase #4	$88.27	12.105%	$98.9551	$98.96	$98.95	$99.00
Purchase #5	$150.76	7.263%	$161.7097	$161.71	$161.70	$161.70
Purchase #6	$71.35	9.588%	$78.191	$78.19	$78.20	$78.20
Purchase #7	$206.94	3.181%	$213.5228	$213.52	$213.50	$213.50
7 purchase totals =	$863.42		$931.5426	$931.55	$931.55	$931.50