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	$91.28	13.366%	$103.4805	$103.48	$103.50	$103.50
Purchase #2	$101.81	10.437%	$112.4359	$112.44	$112.45	$112.40
Purchase #3	$117.91	11.467%	$131.4307	$131.43	$131.45	$131.40
Purchase #4	$63.76	13.710%	$72.5015	$72.50	$72.50	$72.50
Purchase #5	$158.36	6.374%	$168.4539	$168.45	$168.45	$168.50
Purchase #6	$242.74	12.756%	$273.7039	$273.70	$273.70	$273.70
Purchase #7	$150.69	4.220%	$157.0491	$157.05	$157.05	$157.00
7 purchase totals =	$926.55		$1,019.0555	$1,019.05	$1,019.10	$1,019.00