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	$212.27	13.696%	$241.3425	$241.34	$241.35	$241.30
Purchase #2	$30.52	9.461%	$33.4075	$33.41	$33.40	$33.40
Purchase #3	$32.44	9.295%	$35.4553	$35.46	$35.45	$35.50
Purchase #4	$57.90	5.611%	$61.1488	$61.15	$61.15	$61.10
Purchase #5	$224.31	6.463%	$238.8072	$238.81	$238.80	$238.80
Purchase #6	$166.51	3.459%	$172.2696	$172.27	$172.25	$172.30
Purchase #7	$36.73	3.787%	$38.121	$38.12	$38.10	$38.10
7 purchase totals =	$760.68		$820.5519	$820.56	$820.50	$820.50