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	$139.85	7.584%	$150.4562	$150.46	$150.45	$150.50
Purchase #2	$213.73	9.732%	$234.5302	$234.53	$234.55	$234.50
Purchase #3	$237.73	10.874%	$263.5808	$263.58	$263.60	$263.60
Purchase #4	$83.82	8.685%	$91.0998	$91.10	$91.10	$91.10
Purchase #5	$18.89	8.711%	$20.5355	$20.54	$20.55	$20.50
Purchase #6	$155.84	9.642%	$170.8661	$170.87	$170.85	$170.90
Purchase #7	$238.76	12.175%	$267.829	$267.83	$267.85	$267.80
7 purchase totals =	$1,088.62		$1,198.8976	$1,198.91	$1,198.95	$1,198.90