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	$46.41	11.860%	$51.9142	$51.91	$51.90	$51.90
Purchase #2	$83.81	8.211%	$90.6916	$90.69	$90.70	$90.70
Purchase #3	$69.98	6.443%	$74.4888	$74.49	$74.50	$74.50
Purchase #4	$208.83	9.767%	$229.2264	$229.23	$229.25	$229.20
Purchase #5	$235.85	9.591%	$258.4704	$258.47	$258.45	$258.50
Purchase #6	$235.61	5.508%	$248.5874	$248.59	$248.60	$248.60
Purchase #7	$64.96	12.560%	$73.119	$73.12	$73.10	$73.10
7 purchase totals =	$945.45		$1,026.4978	$1,026.50	$1,026.50	$1,026.50