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	$138.85	6.447%	$147.8017	$147.80	$147.80	$147.80
Purchase #2	$110.97	5.355%	$116.9124	$116.91	$116.90	$116.90
Purchase #3	$43.32	4.679%	$45.3469	$45.35	$45.35	$45.30
Purchase #4	$198.48	5.749%	$209.8906	$209.89	$209.90	$209.90
Purchase #5	$125.65	8.243%	$136.0073	$136.01	$136.00	$136.00
Purchase #6	$96.56	4.126%	$100.5441	$100.54	$100.55	$100.50
Purchase #7	$169.98	5.635%	$179.5584	$179.56	$179.55	$179.60
7 purchase totals =	$883.81		$936.0614	$936.06	$936.05	$936.00