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	$39.69	10.155%	$43.7205	$43.72	$43.70	$43.70
Purchase #2	$177.72	3.611%	$184.1375	$184.14	$184.15	$184.10
Purchase #3	$240.77	5.512%	$254.0412	$254.04	$254.05	$254.00
Purchase #4	$83.37	11.761%	$93.1751	$93.18	$93.20	$93.20
Purchase #5	$194.38	8.801%	$211.4874	$211.49	$211.50	$211.50
Purchase #6	$37.69	12.175%	$42.2788	$42.28	$42.30	$42.30
Purchase #7	$156.55	7.375%	$168.0956	$168.10	$168.10	$168.10
7 purchase totals =	$930.17		$996.9361	$996.95	$997.00	$996.90