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	$159.97	12.678%	$180.251	$180.25	$180.25	$180.30
Purchase #2	$244.92	8.776%	$266.4142	$266.41	$266.40	$266.40
Purchase #3	$65.60	11.141%	$72.9085	$72.91	$72.90	$72.90
Purchase #4	$101.28	13.467%	$114.9194	$114.92	$114.90	$114.90
Purchase #5	$35.89	9.505%	$39.3013	$39.30	$39.30	$39.30
Purchase #6	$240.55	10.363%	$265.4782	$265.48	$265.50	$265.50
Purchase #7	$40.76	12.430%	$45.8265	$45.83	$45.85	$45.80
7 purchase totals =	$888.97		$985.0991	$985.10	$985.10	$985.10