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	$45.95	6.400%	$48.8908	$48.89	$48.90	$48.90
Purchase #2	$52.54	8.484%	$56.9975	$57.00	$57.00	$57.00
Purchase #3	$55.73	13.646%	$63.3349	$63.33	$63.35	$63.30
Purchase #4	$71.25	9.797%	$78.2304	$78.23	$78.25	$78.20
Purchase #5	$161.60	5.285%	$170.1406	$170.14	$170.15	$170.10
Purchase #6	$104.52	12.773%	$117.8703	$117.87	$117.85	$117.90
Purchase #7	$243.43	8.618%	$264.4088	$264.41	$264.40	$264.40
7 purchase totals =	$735.02		$799.8733	$799.87	$799.90	$799.80