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	$131.36	11.371%	$146.2969	$146.30	$146.30	$146.30
Purchase #2	$56.39	13.143%	$63.8013	$63.80	$63.80	$63.80
Purchase #3	$133.54	3.569%	$138.306	$138.31	$138.30	$138.30
Purchase #4	$244.93	5.330%	$257.9848	$257.98	$258.00	$258.00
Purchase #5	$56.37	4.857%	$59.1079	$59.11	$59.10	$59.10
Purchase #6	$114.76	8.768%	$124.8222	$124.82	$124.80	$124.80
Purchase #7	$191.48	12.590%	$215.5873	$215.59	$215.60	$215.60
7 purchase totals =	$928.83		$1,005.9064	$1,005.91	$1,005.90	$1,005.90