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	$67.93	7.146%	$72.7843	$72.78	$72.80	$72.80
Purchase #2	$100.25	13.329%	$113.6123	$113.61	$113.60	$113.60
Purchase #3	$18.59	11.102%	$20.6539	$20.65	$20.65	$20.70
Purchase #4	$60.51	7.317%	$64.9375	$64.94	$64.95	$64.90
Purchase #5	$199.98	5.463%	$210.9049	$210.90	$210.90	$210.90
Purchase #6	$195.54	9.858%	$214.8163	$214.82	$214.80	$214.80
Purchase #7	$87.29	4.681%	$91.376	$91.38	$91.40	$91.40
7 purchase totals =	$730.09		$789.0852	$789.08	$789.10	$789.10