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	$12.79	5.428%	$13.4842	$13.48	$13.50	$13.50
Purchase #2	$155.34	12.310%	$174.4624	$174.46	$174.45	$174.50
Purchase #3	$70.31	7.378%	$75.4975	$75.50	$75.50	$75.50
Purchase #4	$52.93	11.459%	$58.9952	$59.00	$59.00	$59.00
Purchase #5	$32.59	10.580%	$36.038	$36.04	$36.05	$36.00
Purchase #6	$8.35	6.726%	$8.9116	$8.91	$8.90	$8.90
Purchase #7	$116.40	12.113%	$130.4995	$130.50	$130.50	$130.50
7 purchase totals =	$448.71		$497.8884	$497.89	$497.90	$497.90