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	$35.26	5.666%	$37.2578	$37.26	$37.25	$37.30
Purchase #2	$105.41	13.679%	$119.829	$119.83	$119.85	$119.80
Purchase #3	$157.49	13.744%	$179.1354	$179.14	$179.15	$179.10
Purchase #4	$179.75	8.652%	$195.302	$195.30	$195.30	$195.30
Purchase #5	$39.56	9.338%	$43.2541	$43.25	$43.25	$43.30
Purchase #6	$39.31	3.254%	$40.5891	$40.59	$40.60	$40.60
Purchase #7	$47.28	9.479%	$51.7617	$51.76	$51.75	$51.80
7 purchase totals =	$604.06		$667.1291	$667.13	$667.15	$667.20