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	$81.47	10.276%	$89.8419	$89.84	$89.85	$89.80
Purchase #2	$205.91	9.466%	$225.4014	$225.40	$225.40	$225.40
Purchase #3	$184.63	5.830%	$195.3939	$195.39	$195.40	$195.40
Purchase #4	$200.30	11.352%	$223.0381	$223.04	$223.05	$223.00
Purchase #5	$244.64	5.378%	$257.7967	$257.80	$257.80	$257.80
Purchase #6	$124.69	6.285%	$132.5268	$132.53	$132.55	$132.50
Purchase #7	$40.52	5.825%	$42.8803	$42.88	$42.90	$42.90
7 purchase totals =	$1,082.16		$1,166.8791	$1,166.88	$1,166.95	$1,166.80