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	$170.84	12.854%	$192.7998	$192.80	$192.80	$192.80
Purchase #2	$243.44	11.494%	$271.421	$271.42	$271.40	$271.40
Purchase #3	$48.81	6.790%	$52.1242	$52.12	$52.10	$52.10
Purchase #4	$96.90	8.866%	$105.4912	$105.49	$105.50	$105.50
Purchase #5	$153.32	7.359%	$164.6028	$164.60	$164.60	$164.60
Purchase #6	$31.59	3.305%	$32.634	$32.63	$32.65	$32.60
Purchase #7	$98.91	11.134%	$109.9226	$109.92	$109.90	$109.90
7 purchase totals =	$843.81		$928.9956	$928.98	$928.95	$928.90