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	$243.33	9.734%	$267.0157	$267.02	$267.00	$267.00
Purchase #2	$36.45	10.468%	$40.2656	$40.27	$40.25	$40.30
Purchase #3	$18.49	11.456%	$20.6082	$20.61	$20.60	$20.60
Purchase #4	$109.52	3.199%	$113.0235	$113.02	$113.00	$113.00
Purchase #5	$182.36	8.604%	$198.0503	$198.05	$198.05	$198.10
Purchase #6	$198.84	10.418%	$219.5552	$219.56	$219.55	$219.60
Purchase #7	$108.33	11.206%	$120.4695	$120.47	$120.45	$120.50
7 purchase totals =	$897.32		$978.9880	$979.00	$978.90	$979.10