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	$80.93	6.149%	$85.9064	$85.91	$85.90	$85.90
Purchase #2	$65.71	5.738%	$69.4804	$69.48	$69.50	$69.50
Purchase #3	$179.91	5.619%	$190.0191	$190.02	$190.00	$190.00
Purchase #4	$108.69	7.202%	$116.5179	$116.52	$116.50	$116.50
Purchase #5	$85.42	7.577%	$91.8923	$91.89	$91.90	$91.90
Purchase #6	$90.71	8.614%	$98.5238	$98.52	$98.50	$98.50
Purchase #7	$245.72	7.647%	$264.5102	$264.51	$264.50	$264.50
7 purchase totals =	$857.09		$916.8501	$916.85	$916.80	$916.80