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	$96.61	4.871%	$101.3159	$101.32	$101.30	$101.30
Purchase #2	$196.73	13.739%	$223.7587	$223.76	$223.75	$223.80
Purchase #3	$97.62	3.381%	$100.9205	$100.92	$100.90	$100.90
Purchase #4	$219.46	9.551%	$240.4206	$240.42	$240.40	$240.40
Purchase #5	$53.61	7.222%	$57.4817	$57.48	$57.50	$57.50
Purchase #6	$47.32	9.129%	$51.6398	$51.64	$51.65	$51.60
Purchase #7	$75.43	7.706%	$81.2426	$81.24	$81.25	$81.20
7 purchase totals =	$786.78		$856.7798	$856.78	$856.75	$856.70