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	$160.50	7.295%	$172.2085	$172.21	$172.20	$172.20
Purchase #2	$248.90	8.671%	$270.4821	$270.48	$270.50	$270.50
Purchase #3	$215.77	10.404%	$238.2187	$238.22	$238.20	$238.20
Purchase #4	$78.87	9.853%	$86.6411	$86.64	$86.65	$86.60
Purchase #5	$230.57	13.307%	$261.2519	$261.25	$261.25	$261.30
Purchase #6	$224.55	6.572%	$239.3074	$239.31	$239.30	$239.30
Purchase #7	$98.38	11.589%	$109.7813	$109.78	$109.80	$109.80
7 purchase totals =	$1,257.54		$1,377.8910	$1,377.89	$1,377.90	$1,377.90