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	$185.41	8.214%	$200.6396	$200.64	$200.65	$200.60
Purchase #2	$89.39	7.554%	$96.1425	$96.14	$96.15	$96.10
Purchase #3	$161.80	9.463%	$177.1111	$177.11	$177.10	$177.10
Purchase #4	$36.43	12.293%	$40.9083	$40.91	$40.90	$40.90
Purchase #5	$10.48	8.547%	$11.3757	$11.38	$11.40	$11.40
Purchase #6	$39.31	11.288%	$43.7473	$43.75	$43.75	$43.70
Purchase #7	$118.75	4.291%	$123.8456	$123.85	$123.85	$123.80
7 purchase totals =	$641.57		$693.7701	$693.78	$693.80	$693.60