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	$112.56	5.597%	$118.86	$118.86	$118.85	$118.90
Purchase #2	$68.67	12.686%	$77.3815	$77.38	$77.40	$77.40
Purchase #3	$92.56	4.134%	$96.3864	$96.39	$96.40	$96.40
Purchase #4	$238.57	6.178%	$253.3089	$253.31	$253.30	$253.30
Purchase #5	$152.56	13.600%	$173.3082	$173.31	$173.30	$173.30
Purchase #6	$12.61	9.619%	$13.823	$13.82	$13.80	$13.80
Purchase #7	$142.30	3.860%	$147.7928	$147.79	$147.80	$147.80
7 purchase totals =	$819.83		$880.8608	$880.86	$880.85	$880.90