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	$91.71	9.296%	$100.2354	$100.24	$100.25	$100.20
Purchase #2	$136.61	13.753%	$155.398	$155.40	$155.40	$155.40
Purchase #3	$205.52	5.846%	$217.5347	$217.53	$217.55	$217.50
Purchase #4	$219.38	11.209%	$243.9703	$243.97	$243.95	$244.00
Purchase #5	$137.49	3.610%	$142.4534	$142.45	$142.45	$142.50
Purchase #6	$65.73	6.732%	$70.1549	$70.15	$70.15	$70.20
Purchase #7	$196.89	13.430%	$223.3323	$223.33	$223.35	$223.30
7 purchase totals =	$1,053.33		$1,153.0790	$1,153.07	$1,153.10	$1,153.10