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	$65.52	3.639%	$67.9043	$67.90	$67.90	$67.90
Purchase #2	$58.42	9.843%	$64.1703	$64.17	$64.15	$64.20
Purchase #3	$200.52	13.712%	$228.0153	$228.02	$228.00	$228.00
Purchase #4	$58.47	4.500%	$61.1012	$61.10	$61.10	$61.10
Purchase #5	$220.83	3.475%	$228.5038	$228.50	$228.50	$228.50
Purchase #6	$16.66	10.180%	$18.356	$18.36	$18.35	$18.40
Purchase #7	$236.92	13.869%	$269.7784	$269.78	$269.80	$269.80
7 purchase totals =	$857.34		$937.8293	$937.83	$937.80	$937.90