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	$35.54	10.195%	$39.1633	$39.16	$39.15	$39.20
Purchase #2	$30.65	3.689%	$31.7807	$31.78	$31.80	$31.80
Purchase #3	$76.69	9.414%	$83.9096	$83.91	$83.90	$83.90
Purchase #4	$243.67	10.336%	$268.8557	$268.86	$268.85	$268.90
Purchase #5	$57.46	8.186%	$62.1637	$62.16	$62.15	$62.20
Purchase #6	$231.61	11.386%	$257.9811	$257.98	$258.00	$258.00
Purchase #7	$94.30	11.647%	$105.2831	$105.28	$105.30	$105.30
7 purchase totals =	$769.92		$849.1372	$849.13	$849.15	$849.30