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	$123.37	10.370%	$136.1635	$136.16	$136.15	$136.20
Purchase #2	$108.50	13.430%	$123.0716	$123.07	$123.05	$123.10
Purchase #3	$46.61	9.109%	$50.8557	$50.86	$50.85	$50.90
Purchase #4	$30.38	6.374%	$32.3164	$32.32	$32.30	$32.30
Purchase #5	$79.62	7.571%	$85.648	$85.65	$85.65	$85.60
Purchase #6	$82.32	13.600%	$93.5155	$93.52	$93.50	$93.50
Purchase #7	$222.97	11.257%	$248.0697	$248.07	$248.05	$248.10
7 purchase totals =	$693.77		$769.6404	$769.65	$769.55	$769.70