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	$5.40	7.704%	$5.816	$5.82	$5.80	$5.80
Purchase #2	$109.80	8.579%	$119.2197	$119.22	$119.20	$119.20
Purchase #3	$82.58	12.661%	$93.0355	$93.04	$93.05	$93.00
Purchase #4	$140.93	3.610%	$146.0176	$146.02	$146.00	$146.00
Purchase #5	$28.72	11.842%	$32.121	$32.12	$32.10	$32.10
Purchase #6	$182.98	7.419%	$196.5553	$196.56	$196.55	$196.60
Purchase #7	$112.93	9.392%	$123.5364	$123.54	$123.55	$123.50
7 purchase totals =	$663.34		$716.3015	$716.32	$716.25	$716.20