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	$83.77	4.230%	$87.3135	$87.31	$87.30	$87.30
Purchase #2	$136.89	12.453%	$153.9369	$153.94	$153.95	$153.90
Purchase #3	$139.64	12.614%	$157.2542	$157.25	$157.25	$157.30
Purchase #4	$179.97	11.418%	$200.519	$200.52	$200.50	$200.50
Purchase #5	$91.53	5.630%	$96.6831	$96.68	$96.70	$96.70
Purchase #6	$222.60	12.473%	$250.3649	$250.36	$250.35	$250.40
Purchase #7	$33.91	10.830%	$37.5825	$37.58	$37.60	$37.60
7 purchase totals =	$888.31		$983.6541	$983.64	$983.65	$983.70