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	$60.58	10.143%	$66.7246	$66.72	$66.70	$66.70
Purchase #2	$76.32	8.578%	$82.8667	$82.87	$82.85	$82.90
Purchase #3	$203.83	12.303%	$228.9072	$228.91	$228.90	$228.90
Purchase #4	$216.51	12.333%	$243.2122	$243.21	$243.20	$243.20
Purchase #5	$245.61	11.364%	$273.5211	$273.52	$273.50	$273.50
Purchase #6	$191.77	9.756%	$210.4791	$210.48	$210.50	$210.50
Purchase #7	$197.59	3.209%	$203.9307	$203.93	$203.95	$203.90
7 purchase totals =	$1,192.21		$1,309.6416	$1,309.64	$1,309.60	$1,309.60