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	$59.91	4.187%	$62.4184	$62.42	$62.40	$62.40
Purchase #2	$125.64	3.394%	$129.9042	$129.90	$129.90	$129.90
Purchase #3	$98.64	6.591%	$105.1414	$105.14	$105.15	$105.10
Purchase #4	$75.35	7.266%	$80.8249	$80.82	$80.80	$80.80
Purchase #5	$156.91	11.157%	$174.4164	$174.42	$174.40	$174.40
Purchase #6	$89.30	4.686%	$93.4846	$93.48	$93.50	$93.50
Purchase #7	$33.51	10.791%	$37.1261	$37.13	$37.15	$37.10
7 purchase totals =	$639.26		$683.3160	$683.31	$683.30	$683.20