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	$186.66	6.671%	$199.1121	$199.11	$199.10	$199.10
Purchase #2	$57.91	5.814%	$61.2769	$61.28	$61.30	$61.30
Purchase #3	$123.75	10.282%	$136.474	$136.47	$136.45	$136.50
Purchase #4	$179.43	8.354%	$194.4196	$194.42	$194.40	$194.40
Purchase #5	$53.80	6.737%	$57.4245	$57.42	$57.40	$57.40
Purchase #6	$41.85	3.663%	$43.383	$43.38	$43.40	$43.40
Purchase #7	$143.62	6.454%	$152.8892	$152.89	$152.90	$152.90
7 purchase totals =	$787.02		$844.9793	$844.97	$844.95	$845.00