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	$6.75	10.512%	$7.4596	$7.46	$7.45	$7.50
Purchase #2	$234.42	7.228%	$251.3639	$251.36	$251.35	$251.40
Purchase #3	$148.39	10.810%	$164.431	$164.43	$164.45	$164.40
Purchase #4	$194.86	3.362%	$201.4112	$201.41	$201.40	$201.40
Purchase #5	$39.38	4.275%	$41.0635	$41.06	$41.05	$41.10
Purchase #6	$226.80	10.494%	$250.6004	$250.60	$250.60	$250.60
Purchase #7	$57.47	3.487%	$59.474	$59.47	$59.45	$59.50
7 purchase totals =	$908.07		$975.8036	$975.79	$975.75	$975.90