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	$110.98	13.822%	$126.3197	$126.32	$126.30	$126.30
Purchase #2	$168.26	12.607%	$189.4725	$189.47	$189.45	$189.50
Purchase #3	$196.85	9.488%	$215.5271	$215.53	$215.55	$215.50
Purchase #4	$62.29	6.865%	$66.5662	$66.57	$66.55	$66.60
Purchase #5	$224.57	4.165%	$233.9233	$233.92	$233.90	$233.90
Purchase #6	$250.56	13.829%	$285.2099	$285.21	$285.20	$285.20
Purchase #7	$162.46	3.709%	$168.4856	$168.49	$168.50	$168.50
7 purchase totals =	$1,175.97		$1,285.5043	$1,285.51	$1,285.45	$1,285.50