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	$141.49	12.738%	$159.513	$159.51	$159.50	$159.50
Purchase #2	$15.91	6.169%	$16.8915	$16.89	$16.90	$16.90
Purchase #3	$87.42	12.755%	$98.5704	$98.57	$98.55	$98.60
Purchase #4	$215.69	12.873%	$243.4558	$243.46	$243.45	$243.50
Purchase #5	$13.56	13.520%	$15.3933	$15.39	$15.40	$15.40
Purchase #6	$116.79	12.232%	$131.0758	$131.08	$131.10	$131.10
Purchase #7	$137.86	7.285%	$147.9031	$147.90	$147.90	$147.90
7 purchase totals =	$728.72		$812.8029	$812.80	$812.80	$812.90