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	$119.62	11.323%	$133.1646	$133.16	$133.15	$133.20
Purchase #2	$198.71	11.141%	$220.8483	$220.85	$220.85	$220.80
Purchase #3	$55.64	7.203%	$59.6477	$59.65	$59.65	$59.60
Purchase #4	$132.34	6.280%	$140.651	$140.65	$140.65	$140.70
Purchase #5	$207.66	10.564%	$229.5972	$229.60	$229.60	$229.60
Purchase #6	$105.39	3.766%	$109.359	$109.36	$109.35	$109.40
Purchase #7	$36.89	3.133%	$38.0458	$38.05	$38.05	$38.00
7 purchase totals =	$856.25		$931.3136	$931.32	$931.30	$931.30