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	$198.36	10.498%	$219.1838	$219.18	$219.20	$219.20
Purchase #2	$145.85	7.182%	$156.3249	$156.32	$156.30	$156.30
Purchase #3	$211.49	6.228%	$224.6616	$224.66	$224.65	$224.70
Purchase #4	$82.86	3.264%	$85.5646	$85.56	$85.55	$85.60
Purchase #5	$145.68	12.738%	$164.2367	$164.24	$164.25	$164.20
Purchase #6	$74.69	4.763%	$78.2475	$78.25	$78.25	$78.20
Purchase #7	$64.44	4.514%	$67.3488	$67.35	$67.35	$67.30
7 purchase totals =	$923.37		$995.5679	$995.56	$995.55	$995.50