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	$187.69	9.515%	$205.5487	$205.55	$205.55	$205.50
Purchase #2	$59.79	11.405%	$66.609	$66.61	$66.60	$66.60
Purchase #3	$79.60	11.840%	$89.0246	$89.02	$89.00	$89.00
Purchase #4	$83.26	5.641%	$87.9567	$87.96	$87.95	$88.00
Purchase #5	$225.72	7.795%	$243.3149	$243.31	$243.30	$243.30
Purchase #6	$87.46	13.746%	$99.4823	$99.48	$99.50	$99.50
Purchase #7	$34.71	10.790%	$38.4552	$38.46	$38.45	$38.50
7 purchase totals =	$758.23		$830.3914	$830.39	$830.35	$830.40