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	$178.93	5.107%	$188.068	$188.07	$188.05	$188.10
Purchase #2	$84.97	6.375%	$90.3868	$90.39	$90.40	$90.40
Purchase #3	$72.44	4.659%	$75.815	$75.82	$75.80	$75.80
Purchase #4	$111.91	11.109%	$124.3421	$124.34	$124.35	$124.30
Purchase #5	$167.98	13.502%	$190.6607	$190.66	$190.65	$190.70
Purchase #6	$128.56	11.122%	$142.8584	$142.86	$142.85	$142.90
Purchase #7	$87.81	13.445%	$99.6161	$99.62	$99.60	$99.60
7 purchase totals =	$832.60		$911.7471	$911.76	$911.70	$911.80