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	$114.54	8.480%	$124.253	$124.25	$124.25	$124.30
Purchase #2	$124.59	13.850%	$141.8457	$141.85	$141.85	$141.80
Purchase #3	$246.63	10.744%	$273.1279	$273.13	$273.15	$273.10
Purchase #4	$36.59	7.472%	$39.324	$39.32	$39.30	$39.30
Purchase #5	$70.94	9.296%	$77.5346	$77.53	$77.55	$77.50
Purchase #6	$90.90	6.568%	$96.8703	$96.87	$96.85	$96.90
Purchase #7	$50.93	11.718%	$56.898	$56.90	$56.90	$56.90
7 purchase totals =	$735.12		$809.8535	$809.85	$809.85	$809.80