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	$38.49	9.860%	$42.2851	$42.29	$42.30	$42.30
Purchase #2	$27.89	12.337%	$31.3308	$31.33	$31.35	$31.30
Purchase #3	$213.76	3.674%	$221.6135	$221.61	$221.60	$221.60
Purchase #4	$171.37	13.361%	$194.2667	$194.27	$194.25	$194.30
Purchase #5	$168.95	4.372%	$176.3365	$176.34	$176.35	$176.30
Purchase #6	$209.62	6.178%	$222.5703	$222.57	$222.55	$222.60
Purchase #7	$104.61	3.460%	$108.2295	$108.23	$108.25	$108.20
7 purchase totals =	$934.69		$996.6324	$996.64	$996.65	$996.60