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	$68.46	6.479%	$72.8955	$72.90	$72.90	$72.90
Purchase #2	$173.94	3.231%	$179.56	$179.56	$179.55	$179.60
Purchase #3	$113.66	12.764%	$128.1676	$128.17	$128.15	$128.20
Purchase #4	$196.27	8.719%	$213.3828	$213.38	$213.40	$213.40
Purchase #5	$16.57	7.577%	$17.8255	$17.83	$17.85	$17.80
Purchase #6	$50.44	9.684%	$55.3246	$55.32	$55.30	$55.30
Purchase #7	$187.55	3.705%	$194.4987	$194.50	$194.50	$194.50
7 purchase totals =	$806.89		$861.6547	$861.66	$861.65	$861.70