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	$50.93	12.291%	$57.1898	$57.19	$57.20	$57.20
Purchase #2	$210.46	12.127%	$235.9825	$235.98	$236.00	$236.00
Purchase #3	$47.89	12.474%	$53.8638	$53.86	$53.85	$53.90
Purchase #4	$158.94	12.135%	$178.2274	$178.23	$178.25	$178.20
Purchase #5	$36.74	3.366%	$37.9767	$37.98	$38.00	$38.00
Purchase #6	$188.38	11.172%	$209.4258	$209.43	$209.45	$209.40
Purchase #7	$55.64	7.437%	$59.7779	$59.78	$59.80	$59.80
7 purchase totals =	$748.98		$832.4439	$832.45	$832.55	$832.50