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	$241.67	12.505%	$271.8908	$271.89	$271.90	$271.90
Purchase #2	$194.85	11.312%	$216.8914	$216.89	$216.90	$216.90
Purchase #3	$233.38	4.316%	$243.4527	$243.45	$243.45	$243.50
Purchase #4	$98.91	4.352%	$103.2146	$103.21	$103.20	$103.20
Purchase #5	$61.98	4.502%	$64.7703	$64.77	$64.75	$64.80
Purchase #6	$206.77	9.451%	$226.3118	$226.31	$226.30	$226.30
Purchase #7	$243.51	4.293%	$253.9639	$253.96	$253.95	$254.00
7 purchase totals =	$1,281.07		$1,380.4955	$1,380.48	$1,380.45	$1,380.60