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	$153.37	11.566%	$171.1088	$171.11	$171.10	$171.10
Purchase #2	$35.55	4.416%	$37.1199	$37.12	$37.10	$37.10
Purchase #3	$170.77	13.108%	$193.1545	$193.15	$193.15	$193.20
Purchase #4	$53.44	4.610%	$55.9036	$55.90	$55.90	$55.90
Purchase #5	$53.46	4.212%	$55.7117	$55.71	$55.70	$55.70
Purchase #6	$80.95	11.570%	$90.3159	$90.32	$90.30	$90.30
Purchase #7	$54.85	9.861%	$60.2588	$60.26	$60.25	$60.30
7 purchase totals =	$602.39		$663.5732	$663.57	$663.50	$663.60