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	$69.62	4.562%	$72.7961	$72.80	$72.80	$72.80
Purchase #2	$247.28	6.319%	$262.9056	$262.91	$262.90	$262.90
Purchase #3	$136.33	11.611%	$152.1593	$152.16	$152.15	$152.20
Purchase #4	$150.33	4.684%	$157.3715	$157.37	$157.35	$157.40
Purchase #5	$39.85	13.734%	$45.323	$45.32	$45.30	$45.30
Purchase #6	$120.41	6.645%	$128.4112	$128.41	$128.40	$128.40
Purchase #7	$149.65	10.189%	$164.8978	$164.90	$164.90	$164.90
7 purchase totals =	$913.47		$983.8645	$983.87	$983.80	$983.90