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	$50.87	4.109%	$52.9602	$52.96	$52.95	$53.00
Purchase #2	$29.96	11.149%	$33.3002	$33.30	$33.30	$33.30
Purchase #3	$184.70	12.737%	$208.2252	$208.23	$208.25	$208.20
Purchase #4	$71.71	9.641%	$78.6236	$78.62	$78.60	$78.60
Purchase #5	$197.80	13.402%	$224.3092	$224.31	$224.30	$224.30
Purchase #6	$88.72	12.394%	$99.716	$99.72	$99.70	$99.70
Purchase #7	$213.79	5.132%	$224.7617	$224.76	$224.75	$224.80
7 purchase totals =	$837.55		$921.8961	$921.90	$921.85	$921.90