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	$89.29	11.328%	$99.4048	$99.40	$99.40	$99.40
Purchase #2	$86.28	5.179%	$90.7484	$90.75	$90.75	$90.70
Purchase #3	$236.40	5.382%	$249.123	$249.12	$249.10	$249.10
Purchase #4	$144.51	11.158%	$160.6344	$160.63	$160.65	$160.60
Purchase #5	$30.70	3.584%	$31.8003	$31.80	$31.80	$31.80
Purchase #6	$191.95	6.164%	$203.7818	$203.78	$203.80	$203.80
Purchase #7	$70.46	11.321%	$78.4368	$78.44	$78.45	$78.40
7 purchase totals =	$849.59		$913.9295	$913.92	$913.95	$913.80