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	$62.57	6.392%	$66.5695	$66.57	$66.55	$66.60
Purchase #2	$85.87	12.294%	$96.4269	$96.43	$96.45	$96.40
Purchase #3	$171.53	9.148%	$187.2216	$187.22	$187.20	$187.20
Purchase #4	$146.27	9.570%	$160.268	$160.27	$160.25	$160.30
Purchase #5	$100.89	8.130%	$109.0924	$109.09	$109.10	$109.10
Purchase #6	$157.62	8.449%	$170.9373	$170.94	$170.95	$170.90
Purchase #7	$112.38	10.196%	$123.8383	$123.84	$123.85	$123.80
7 purchase totals =	$837.13		$914.3540	$914.36	$914.35	$914.30