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	$95.54	4.388%	$99.7323	$99.73	$99.75	$99.70
Purchase #2	$53.43	6.454%	$56.8784	$56.88	$56.90	$56.90
Purchase #3	$190.25	9.529%	$208.3789	$208.38	$208.40	$208.40
Purchase #4	$95.76	6.862%	$102.3311	$102.33	$102.35	$102.30
Purchase #5	$48.58	12.469%	$54.6374	$54.64	$54.65	$54.60
Purchase #6	$106.36	12.170%	$119.304	$119.30	$119.30	$119.30
Purchase #7	$148.32	13.322%	$168.0792	$168.08	$168.10	$168.10
7 purchase totals =	$738.24		$809.3413	$809.34	$809.45	$809.30