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	$10.67	11.665%	$11.9147	$11.91	$11.90	$11.90
Purchase #2	$162.50	9.873%	$178.5436	$178.54	$178.55	$178.50
Purchase #3	$90.63	13.602%	$102.9575	$102.96	$102.95	$103.00
Purchase #4	$64.39	7.761%	$69.3873	$69.39	$69.40	$69.40
Purchase #5	$188.38	5.384%	$198.5224	$198.52	$198.50	$198.50
Purchase #6	$156.90	9.446%	$171.7208	$171.72	$171.70	$171.70
Purchase #7	$175.29	13.602%	$199.1329	$199.13	$199.15	$199.10
7 purchase totals =	$848.76		$932.1792	$932.17	$932.15	$932.10