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	$113.53	6.379%	$120.7721	$120.77	$120.75	$120.80
Purchase #2	$136.28	10.235%	$150.2283	$150.23	$150.25	$150.20
Purchase #3	$31.38	4.379%	$32.7541	$32.75	$32.75	$32.80
Purchase #4	$168.69	4.823%	$176.8259	$176.83	$176.85	$176.80
Purchase #5	$104.33	7.275%	$111.92	$111.92	$111.90	$111.90
Purchase #6	$5.29	10.206%	$5.8299	$5.83	$5.85	$5.80
Purchase #7	$232.72	7.866%	$251.0258	$251.03	$251.05	$251.00
7 purchase totals =	$792.22		$849.3561	$849.36	$849.40	$849.30