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	$90.36	11.283%	$100.5553	$100.56	$100.55	$100.60
Purchase #2	$66.55	6.424%	$70.8252	$70.83	$70.85	$70.80
Purchase #3	$82.89	9.226%	$90.5374	$90.54	$90.55	$90.50
Purchase #4	$68.70	7.530%	$73.8731	$73.87	$73.85	$73.90
Purchase #5	$205.81	9.481%	$225.3228	$225.32	$225.30	$225.30
Purchase #6	$21.37	6.146%	$22.6834	$22.68	$22.70	$22.70
Purchase #7	$169.88	9.617%	$186.2174	$186.22	$186.20	$186.20
7 purchase totals =	$705.56		$770.0146	$770.02	$770.00	$770.00