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	$231.54	7.401%	$248.6763	$248.68	$248.70	$248.70
Purchase #2	$80.96	12.694%	$91.2371	$91.24	$91.25	$91.20
Purchase #3	$134.46	10.713%	$148.8647	$148.86	$148.85	$148.90
Purchase #4	$188.61	4.216%	$196.5618	$196.56	$196.55	$196.60
Purchase #5	$140.82	6.523%	$150.0057	$150.01	$150.00	$150.00
Purchase #6	$6.85	9.283%	$7.4859	$7.49	$7.50	$7.50
Purchase #7	$65.98	7.189%	$70.7233	$70.72	$70.70	$70.70
7 purchase totals =	$849.22		$913.5548	$913.56	$913.55	$913.60