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	$36.89	5.813%	$39.0344	$39.03	$39.05	$39.00
Purchase #2	$73.34	6.111%	$77.8218	$77.82	$77.80	$77.80
Purchase #3	$162.40	4.550%	$169.7892	$169.79	$169.80	$169.80
Purchase #4	$124.72	5.392%	$131.4449	$131.44	$131.45	$131.40
Purchase #5	$213.72	7.869%	$230.5376	$230.54	$230.55	$230.50
Purchase #6	$29.88	7.356%	$32.078	$32.08	$32.10	$32.10
Purchase #7	$83.74	7.745%	$90.2257	$90.23	$90.25	$90.20
7 purchase totals =	$724.69		$770.9316	$770.93	$771.00	$770.80