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	$70.48	13.694%	$80.1315	$80.13	$80.15	$80.10
Purchase #2	$40.33	12.686%	$45.4463	$45.45	$45.45	$45.40
Purchase #3	$237.42	5.308%	$250.0223	$250.02	$250.00	$250.00
Purchase #4	$54.40	8.523%	$59.0365	$59.04	$59.05	$59.00
Purchase #5	$196.30	8.171%	$212.3397	$212.34	$212.35	$212.30
Purchase #6	$204.42	6.435%	$217.5744	$217.57	$217.55	$217.60
Purchase #7	$157.80	12.364%	$177.3104	$177.31	$177.30	$177.30
7 purchase totals =	$961.15		$1,041.8611	$1,041.86	$1,041.85	$1,041.70