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	$189.86	9.873%	$208.6049	$208.60	$208.60	$208.60
Purchase #2	$220.35	13.144%	$249.3128	$249.31	$249.30	$249.30
Purchase #3	$35.73	13.782%	$40.6543	$40.65	$40.65	$40.70
Purchase #4	$224.53	12.833%	$253.3439	$253.34	$253.35	$253.30
Purchase #5	$94.57	6.362%	$100.5865	$100.59	$100.60	$100.60
Purchase #6	$43.29	3.386%	$44.7558	$44.76	$44.75	$44.80
Purchase #7	$31.94	6.776%	$34.1043	$34.10	$34.10	$34.10
7 purchase totals =	$840.27		$931.3625	$931.35	$931.35	$931.40