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	$10.31	5.227%	$10.8489	$10.85	$10.85	$10.80
Purchase #2	$147.81	8.529%	$160.4167	$160.42	$160.40	$160.40
Purchase #3	$222.54	11.846%	$248.9021	$248.90	$248.90	$248.90
Purchase #4	$120.31	11.431%	$134.0626	$134.06	$134.05	$134.10
Purchase #5	$152.56	8.131%	$164.9647	$164.96	$164.95	$165.00
Purchase #6	$37.47	13.674%	$42.5936	$42.59	$42.60	$42.60
Purchase #7	$209.98	11.616%	$234.3713	$234.37	$234.35	$234.40
7 purchase totals =	$900.98		$996.1599	$996.15	$996.10	$996.20