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	$28.98	10.780%	$32.104	$32.10	$32.10	$32.10
Purchase #2	$211.63	6.660%	$225.7246	$225.72	$225.70	$225.70
Purchase #3	$120.78	6.301%	$128.3903	$128.39	$128.40	$128.40
Purchase #4	$240.29	5.778%	$254.174	$254.17	$254.15	$254.20
Purchase #5	$250.78	13.607%	$284.9036	$284.90	$284.90	$284.90
Purchase #6	$149.97	11.285%	$166.8941	$166.89	$166.90	$166.90
Purchase #7	$38.97	6.174%	$41.376	$41.38	$41.40	$41.40
7 purchase totals =	$1,041.40		$1,133.5666	$1,133.55	$1,133.55	$1,133.60