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	$122.37	4.835%	$128.2866	$128.29	$128.30	$128.30
Purchase #2	$224.89	10.629%	$248.7936	$248.79	$248.80	$248.80
Purchase #3	$85.74	4.334%	$89.456	$89.46	$89.45	$89.50
Purchase #4	$30.83	5.337%	$32.4754	$32.48	$32.50	$32.50
Purchase #5	$143.56	5.111%	$150.8974	$150.90	$150.90	$150.90
Purchase #6	$71.36	8.268%	$77.26	$77.26	$77.25	$77.30
Purchase #7	$119.55	7.597%	$128.6322	$128.63	$128.65	$128.60
7 purchase totals =	$798.30		$855.8012	$855.81	$855.85	$855.90