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	$20.63	4.392%	$21.5361	$21.54	$21.55	$21.50
Purchase #2	$174.82	3.407%	$180.7761	$180.78	$180.80	$180.80
Purchase #3	$212.97	3.243%	$219.8766	$219.88	$219.90	$219.90
Purchase #4	$17.55	5.778%	$18.564	$18.56	$18.55	$18.60
Purchase #5	$90.53	4.590%	$94.6853	$94.69	$94.70	$94.70
Purchase #6	$80.46	11.794%	$89.9495	$89.95	$89.95	$89.90
Purchase #7	$157.48	11.842%	$176.1288	$176.13	$176.15	$176.10
7 purchase totals =	$754.44		$801.5164	$801.53	$801.60	$801.50