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	$64.89	9.769%	$71.2291	$71.23	$71.25	$71.20
Purchase #2	$133.81	4.558%	$139.9091	$139.91	$139.90	$139.90
Purchase #3	$27.94	12.820%	$31.5219	$31.52	$31.50	$31.50
Purchase #4	$109.48	6.119%	$116.1791	$116.18	$116.20	$116.20
Purchase #5	$101.95	7.416%	$109.5106	$109.51	$109.50	$109.50
Purchase #6	$204.96	9.739%	$224.9211	$224.92	$224.90	$224.90
Purchase #7	$80.98	12.720%	$91.2807	$91.28	$91.30	$91.30
7 purchase totals =	$724.01		$784.5516	$784.55	$784.55	$784.50