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	$34.37	7.680%	$37.0096	$37.01	$37.00	$37.00
Purchase #2	$234.76	6.857%	$250.8575	$250.86	$250.85	$250.90
Purchase #3	$65.46	10.608%	$72.404	$72.40	$72.40	$72.40
Purchase #4	$70.84	3.533%	$73.3428	$73.34	$73.35	$73.30
Purchase #5	$58.50	10.703%	$64.7613	$64.76	$64.75	$64.80
Purchase #6	$234.32	8.787%	$254.9097	$254.91	$254.90	$254.90
Purchase #7	$35.52	13.549%	$40.3326	$40.33	$40.35	$40.30
7 purchase totals =	$733.77		$793.6175	$793.61	$793.60	$793.60