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	$154.83	5.221%	$162.9137	$162.91	$162.90	$162.90
Purchase #2	$91.64	5.339%	$96.5327	$96.53	$96.55	$96.50
Purchase #3	$154.85	9.448%	$169.4802	$169.48	$169.50	$169.50
Purchase #4	$187.52	6.545%	$199.7932	$199.79	$199.80	$199.80
Purchase #5	$49.69	8.433%	$53.8804	$53.88	$53.90	$53.90
Purchase #6	$37.43	11.648%	$41.7898	$41.79	$41.80	$41.80
Purchase #7	$109.35	6.156%	$116.0816	$116.08	$116.10	$116.10
7 purchase totals =	$785.31		$840.4716	$840.46	$840.55	$840.50