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	$35.38	4.759%	$37.0637	$37.06	$37.05	$37.10
Purchase #2	$98.93	12.417%	$111.2141	$111.21	$111.20	$111.20
Purchase #3	$25.73	11.474%	$28.6823	$28.68	$28.70	$28.70
Purchase #4	$223.60	4.351%	$233.3288	$233.33	$233.35	$233.30
Purchase #5	$68.38	12.650%	$77.0301	$77.03	$77.05	$77.00
Purchase #6	$7.41	5.519%	$7.819	$7.82	$7.80	$7.80
Purchase #7	$150.54	10.815%	$166.8209	$166.82	$166.80	$166.80
7 purchase totals =	$609.97		$661.9589	$661.95	$661.95	$661.90