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	$28.48	9.306%	$31.1303	$31.13	$31.15	$31.10
Purchase #2	$62.74	3.366%	$64.8518	$64.85	$64.85	$64.90
Purchase #3	$66.66	9.390%	$72.9194	$72.92	$72.90	$72.90
Purchase #4	$202.87	10.186%	$223.5343	$223.53	$223.55	$223.50
Purchase #5	$67.98	8.761%	$73.9357	$73.94	$73.95	$73.90
Purchase #6	$174.90	7.423%	$187.8828	$187.88	$187.90	$187.90
Purchase #7	$151.96	11.405%	$169.291	$169.29	$169.30	$169.30
7 purchase totals =	$755.59		$823.5453	$823.54	$823.60	$823.50