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	$39.33	8.499%	$42.6727	$42.67	$42.65	$42.70
Purchase #2	$122.46	7.638%	$131.8135	$131.81	$131.80	$131.80
Purchase #3	$83.77	7.498%	$90.0511	$90.05	$90.05	$90.10
Purchase #4	$181.86	9.691%	$199.4841	$199.48	$199.50	$199.50
Purchase #5	$172.27	4.790%	$180.5217	$180.52	$180.50	$180.50
Purchase #6	$178.57	9.289%	$195.1574	$195.16	$195.15	$195.20
Purchase #7	$229.82	12.251%	$257.9752	$257.98	$258.00	$258.00
7 purchase totals =	$1,008.08		$1,097.6757	$1,097.67	$1,097.65	$1,097.80