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	$18.72	11.122%	$20.802	$20.80	$20.80	$20.80
Purchase #2	$82.25	10.414%	$90.8155	$90.82	$90.80	$90.80
Purchase #3	$149.69	4.553%	$156.5054	$156.51	$156.50	$156.50
Purchase #4	$139.87	11.338%	$155.7285	$155.73	$155.75	$155.70
Purchase #5	$40.25	11.331%	$44.8107	$44.81	$44.80	$44.80
Purchase #6	$136.36	4.530%	$142.5371	$142.54	$142.55	$142.50
Purchase #7	$103.51	6.580%	$110.321	$110.32	$110.30	$110.30
7 purchase totals =	$670.65		$721.5202	$721.53	$721.50	$721.40