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	$30.40	10.507%	$33.5941	$33.59	$33.60	$33.60
Purchase #2	$5.38	6.136%	$5.7101	$5.71	$5.70	$5.70
Purchase #3	$133.91	13.609%	$152.1338	$152.13	$152.15	$152.10
Purchase #4	$105.28	8.339%	$114.0593	$114.06	$114.05	$114.10
Purchase #5	$92.81	11.334%	$103.3291	$103.33	$103.35	$103.30
Purchase #6	$90.44	11.828%	$101.1372	$101.14	$101.15	$101.10
Purchase #7	$87.90	13.468%	$99.7384	$99.74	$99.75	$99.70
7 purchase totals =	$546.12		$609.7020	$609.70	$609.75	$609.60