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	$52.90	12.300%	$59.4067	$59.41	$59.40	$59.40
Purchase #2	$243.34	10.578%	$269.0805	$269.08	$269.10	$269.10
Purchase #3	$16.86	10.576%	$18.6431	$18.64	$18.65	$18.60
Purchase #4	$236.86	12.788%	$267.1497	$267.15	$267.15	$267.10
Purchase #5	$97.41	12.767%	$109.8463	$109.85	$109.85	$109.80
Purchase #6	$41.80	11.139%	$46.4561	$46.46	$46.45	$46.50
Purchase #7	$197.48	13.696%	$224.5269	$224.53	$224.55	$224.50
7 purchase totals =	$886.65		$995.1093	$995.12	$995.15	$995.00