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	$124.86	9.195%	$136.3409	$136.34	$136.35	$136.30
Purchase #2	$140.28	8.384%	$152.0411	$152.04	$152.05	$152.00
Purchase #3	$189.58	11.698%	$211.7571	$211.76	$211.75	$211.80
Purchase #4	$155.73	13.564%	$176.8532	$176.85	$176.85	$176.90
Purchase #5	$89.74	11.275%	$99.8582	$99.86	$99.85	$99.90
Purchase #6	$233.45	5.805%	$247.0018	$247.00	$247.00	$247.00
Purchase #7	$239.50	4.221%	$249.6093	$249.61	$249.60	$249.60
7 purchase totals =	$1,173.14		$1,273.4616	$1,273.46	$1,273.45	$1,273.50