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	$8.67	13.256%	$9.8193	$9.82	$9.80	$9.80
Purchase #2	$78.77	8.318%	$85.3221	$85.32	$85.30	$85.30
Purchase #3	$199.66	11.270%	$222.1617	$222.16	$222.15	$222.20
Purchase #4	$141.56	4.468%	$147.8849	$147.88	$147.90	$147.90
Purchase #5	$125.54	10.668%	$138.9326	$138.93	$138.95	$138.90
Purchase #6	$18.80	3.572%	$19.4715	$19.47	$19.45	$19.50
Purchase #7	$150.76	11.845%	$168.6175	$168.62	$168.60	$168.60
7 purchase totals =	$723.76		$792.2096	$792.20	$792.15	$792.20