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	$30.85	9.859%	$33.8915	$33.89	$33.90	$33.90
Purchase #2	$33.57	11.457%	$37.4161	$37.42	$37.40	$37.40
Purchase #3	$34.43	11.386%	$38.3502	$38.35	$38.35	$38.40
Purchase #4	$171.74	3.424%	$177.6204	$177.62	$177.60	$177.60
Purchase #5	$209.78	7.740%	$226.017	$226.02	$226.00	$226.00
Purchase #6	$179.56	9.282%	$196.2268	$196.23	$196.25	$196.20
Purchase #7	$97.96	7.343%	$105.1532	$105.15	$105.15	$105.20
7 purchase totals =	$757.89		$814.6752	$814.68	$814.65	$814.70