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	$35.40	6.702%	$37.7725	$37.77	$37.75	$37.80
Purchase #2	$134.43	9.412%	$147.0826	$147.08	$147.10	$147.10
Purchase #3	$157.38	4.583%	$164.5927	$164.59	$164.60	$164.60
Purchase #4	$47.54	13.362%	$53.8923	$53.89	$53.90	$53.90
Purchase #5	$25.96	5.570%	$27.406	$27.41	$27.40	$27.40
Purchase #6	$45.46	6.514%	$48.4213	$48.42	$48.40	$48.40
Purchase #7	$99.66	6.761%	$106.398	$106.40	$106.40	$106.40
7 purchase totals =	$545.83		$585.5654	$585.56	$585.55	$585.60