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	$85.97	5.394%	$90.6072	$90.61	$90.60	$90.60
Purchase #2	$238.58	9.350%	$260.8872	$260.89	$260.90	$260.90
Purchase #3	$29.66	10.518%	$32.7796	$32.78	$32.80	$32.80
Purchase #4	$33.33	10.759%	$36.916	$36.92	$36.90	$36.90
Purchase #5	$224.69	4.691%	$235.2302	$235.23	$235.25	$235.20
Purchase #6	$38.35	9.689%	$42.0657	$42.07	$42.05	$42.10
Purchase #7	$63.87	12.765%	$72.023	$72.02	$72.00	$72.00
7 purchase totals =	$714.45		$770.5089	$770.52	$770.50	$770.50