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	$227.66	11.808%	$254.5421	$254.54	$254.55	$254.50
Purchase #2	$213.34	5.351%	$224.7558	$224.76	$224.75	$224.80
Purchase #3	$132.91	11.294%	$147.9209	$147.92	$147.90	$147.90
Purchase #4	$99.70	6.248%	$105.9293	$105.93	$105.95	$105.90
Purchase #5	$164.92	9.644%	$180.8249	$180.82	$180.80	$180.80
Purchase #6	$179.74	5.128%	$188.9571	$188.96	$188.95	$189.00
Purchase #7	$36.62	10.360%	$40.4138	$40.41	$40.40	$40.40
7 purchase totals =	$1,054.89		$1,143.3439	$1,143.34	$1,143.30	$1,143.30