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	$33.98	12.790%	$38.326	$38.33	$38.35	$38.30
Purchase #2	$88.35	12.188%	$99.1181	$99.12	$99.10	$99.10
Purchase #3	$127.79	9.224%	$139.5773	$139.58	$139.60	$139.60
Purchase #4	$103.81	5.214%	$109.2227	$109.22	$109.20	$109.20
Purchase #5	$39.58	12.502%	$44.5283	$44.53	$44.55	$44.50
Purchase #6	$93.43	4.137%	$97.2952	$97.30	$97.30	$97.30
Purchase #7	$139.33	10.400%	$153.8203	$153.82	$153.80	$153.80
7 purchase totals =	$626.27		$681.8879	$681.90	$681.90	$681.80