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	$81.38	7.313%	$87.3313	$87.33	$87.35	$87.30
Purchase #2	$65.51	3.106%	$67.5447	$67.54	$67.55	$67.50
Purchase #3	$49.74	11.189%	$55.3054	$55.31	$55.30	$55.30
Purchase #4	$191.87	4.140%	$199.8134	$199.81	$199.80	$199.80
Purchase #5	$218.82	9.362%	$239.3059	$239.31	$239.30	$239.30
Purchase #6	$58.94	13.648%	$66.9841	$66.98	$67.00	$67.00
Purchase #7	$108.61	3.419%	$112.3234	$112.32	$112.30	$112.30
7 purchase totals =	$774.87		$828.6082	$828.60	$828.60	$828.50