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	$90.38	4.874%	$94.7851	$94.79	$94.80	$94.80
Purchase #2	$183.96	8.309%	$199.2452	$199.25	$199.25	$199.20
Purchase #3	$168.49	11.809%	$188.387	$188.39	$188.40	$188.40
Purchase #4	$36.98	9.628%	$40.5404	$40.54	$40.55	$40.50
Purchase #5	$83.52	7.196%	$89.5301	$89.53	$89.55	$89.50
Purchase #6	$6.77	13.142%	$7.6597	$7.66	$7.65	$7.70
Purchase #7	$180.37	4.462%	$188.4181	$188.42	$188.40	$188.40
7 purchase totals =	$750.47		$808.5656	$808.58	$808.60	$808.50