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	$76.27	7.705%	$82.1466	$82.15	$82.15	$82.10
Purchase #2	$178.46	10.348%	$196.927	$196.93	$196.95	$196.90
Purchase #3	$125.90	11.863%	$140.8355	$140.84	$140.85	$140.80
Purchase #4	$31.35	7.778%	$33.7884	$33.79	$33.80	$33.80
Purchase #5	$178.53	13.796%	$203.16	$203.16	$203.15	$203.20
Purchase #6	$47.50	7.448%	$51.0378	$51.04	$51.05	$51.00
Purchase #7	$112.29	13.490%	$127.4379	$127.44	$127.45	$127.40
7 purchase totals =	$750.30		$835.3332	$835.35	$835.40	$835.20