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	$104.83	3.751%	$108.7622	$108.76	$108.75	$108.80
Purchase #2	$234.94	6.289%	$249.7154	$249.72	$249.70	$249.70
Purchase #3	$82.55	9.855%	$90.6853	$90.69	$90.70	$90.70
Purchase #4	$7.81	7.835%	$8.4219	$8.42	$8.40	$8.40
Purchase #5	$147.71	4.601%	$154.5061	$154.51	$154.50	$154.50
Purchase #6	$89.95	13.349%	$101.9574	$101.96	$101.95	$102.00
Purchase #7	$52.48	12.470%	$59.0243	$59.02	$59.00	$59.00
7 purchase totals =	$720.27		$773.0726	$773.08	$773.00	$773.10