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	$75.71	3.399%	$78.2834	$78.28	$78.30	$78.30
Purchase #2	$46.74	13.112%	$52.8685	$52.87	$52.85	$52.90
Purchase #3	$82.27	10.443%	$90.8615	$90.86	$90.85	$90.90
Purchase #4	$127.73	4.293%	$133.2134	$133.21	$133.20	$133.20
Purchase #5	$13.57	8.459%	$14.7179	$14.72	$14.70	$14.70
Purchase #6	$170.42	11.267%	$189.6212	$189.62	$189.60	$189.60
Purchase #7	$160.89	12.382%	$180.8114	$180.81	$180.80	$180.80
7 purchase totals =	$677.33		$740.3773	$740.37	$740.30	$740.40