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	$72.81	3.447%	$75.3198	$75.32	$75.30	$75.30
Purchase #2	$136.86	7.808%	$147.546	$147.55	$147.55	$147.50
Purchase #3	$39.59	13.431%	$44.9073	$44.91	$44.90	$44.90
Purchase #4	$56.77	13.412%	$64.384	$64.38	$64.40	$64.40
Purchase #5	$61.80	11.337%	$68.8063	$68.81	$68.80	$68.80
Purchase #6	$65.70	9.684%	$72.0624	$72.06	$72.05	$72.10
Purchase #7	$85.50	13.362%	$96.9245	$96.92	$96.90	$96.90
7 purchase totals =	$519.03		$569.9503	$569.95	$569.90	$569.90