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	$134.44	12.331%	$151.0178	$151.02	$151.00	$151.00
Purchase #2	$31.59	7.238%	$33.8765	$33.88	$33.90	$33.90
Purchase #3	$88.33	13.487%	$100.2431	$100.24	$100.25	$100.20
Purchase #4	$175.77	10.593%	$194.3893	$194.39	$194.40	$194.40
Purchase #5	$72.91	5.226%	$76.7203	$76.72	$76.70	$76.70
Purchase #6	$33.50	4.294%	$34.9385	$34.94	$34.95	$34.90
Purchase #7	$63.67	10.776%	$70.5311	$70.53	$70.55	$70.50
7 purchase totals =	$600.21		$661.7166	$661.72	$661.75	$661.60