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	$11.25	5.619%	$11.8821	$11.88	$11.90	$11.90
Purchase #2	$94.88	9.241%	$103.6479	$103.65	$103.65	$103.60
Purchase #3	$240.94	12.654%	$271.4285	$271.43	$271.45	$271.40
Purchase #4	$188.34	5.385%	$198.4821	$198.48	$198.50	$198.50
Purchase #5	$135.93	11.801%	$151.9711	$151.97	$151.95	$152.00
Purchase #6	$18.61	6.437%	$19.8079	$19.81	$19.80	$19.80
Purchase #7	$40.99	3.571%	$42.4538	$42.45	$42.45	$42.50
7 purchase totals =	$730.94		$799.6734	$799.67	$799.70	$799.70