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	$178.35	6.793%	$190.4653	$190.47	$190.45	$190.50
Purchase #2	$76.50	13.451%	$86.79	$86.79	$86.80	$86.80
Purchase #3	$57.72	10.133%	$63.5688	$63.57	$63.55	$63.60
Purchase #4	$194.98	12.864%	$220.0622	$220.06	$220.05	$220.10
Purchase #5	$218.67	11.350%	$243.489	$243.49	$243.50	$243.50
Purchase #6	$64.38	12.553%	$72.4616	$72.46	$72.45	$72.50
Purchase #7	$203.34	5.773%	$215.0788	$215.08	$215.10	$215.10
7 purchase totals =	$993.94		$1,091.9157	$1,091.92	$1,091.90	$1,092.10