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	$33.90	13.547%	$38.4924	$38.49	$38.50	$38.50
Purchase #2	$35.71	6.798%	$38.1376	$38.14	$38.15	$38.10
Purchase #3	$250.68	3.277%	$258.8948	$258.89	$258.90	$258.90
Purchase #4	$91.45	13.518%	$103.8122	$103.81	$103.80	$103.80
Purchase #5	$14.34	7.263%	$15.3815	$15.38	$15.40	$15.40
Purchase #6	$8.56	9.715%	$9.3916	$9.39	$9.40	$9.40
Purchase #7	$94.91	4.642%	$99.3157	$99.32	$99.30	$99.30
7 purchase totals =	$529.55		$563.4258	$563.42	$563.45	$563.40