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	$33.91	10.180%	$37.362	$37.36	$37.35	$37.40
Purchase #2	$17.44	8.786%	$18.9723	$18.97	$18.95	$19.00
Purchase #3	$32.59	10.350%	$35.9631	$35.96	$35.95	$36.00
Purchase #4	$19.31	5.542%	$20.3802	$20.38	$20.40	$20.40
Purchase #5	$100.96	3.398%	$104.3906	$104.39	$104.40	$104.40
Purchase #6	$144.82	5.385%	$152.6186	$152.62	$152.60	$152.60
Purchase #7	$106.44	3.794%	$110.4783	$110.48	$110.50	$110.50
7 purchase totals =	$455.47		$480.1651	$480.16	$480.15	$480.30