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	$171.25	13.178%	$193.8173	$193.82	$193.80	$193.80
Purchase #2	$93.37	6.778%	$99.6986	$99.70	$99.70	$99.70
Purchase #3	$78.54	9.309%	$85.8513	$85.85	$85.85	$85.90
Purchase #4	$75.54	13.270%	$85.5642	$85.56	$85.55	$85.60
Purchase #5	$30.91	3.145%	$31.8821	$31.88	$31.90	$31.90
Purchase #6	$212.59	13.747%	$241.8147	$241.81	$241.80	$241.80
Purchase #7	$138.37	4.365%	$144.4099	$144.41	$144.40	$144.40
7 purchase totals =	$800.57		$883.0381	$883.03	$883.00	$883.10