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	$58.48	8.269%	$63.3157	$63.32	$63.30	$63.30
Purchase #2	$200.89	10.587%	$222.1582	$222.16	$222.15	$222.20
Purchase #3	$219.66	10.839%	$243.4689	$243.47	$243.45	$243.50
Purchase #4	$36.98	4.702%	$38.7188	$38.72	$38.70	$38.70
Purchase #5	$67.99	6.527%	$72.4277	$72.43	$72.45	$72.40
Purchase #6	$21.79	12.267%	$24.463	$24.46	$24.45	$24.50
Purchase #7	$250.74	12.684%	$282.5439	$282.54	$282.55	$282.50
7 purchase totals =	$856.53		$947.0962	$947.10	$947.05	$947.10