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	$40.75	4.835%	$42.7203	$42.72	$42.70	$42.70
Purchase #2	$71.73	9.432%	$78.4956	$78.50	$78.50	$78.50
Purchase #3	$7.53	12.532%	$8.4737	$8.47	$8.45	$8.50
Purchase #4	$43.59	9.131%	$47.5702	$47.57	$47.55	$47.60
Purchase #5	$242.37	11.736%	$270.8145	$270.81	$270.80	$270.80
Purchase #6	$34.85	7.321%	$37.4014	$37.40	$37.40	$37.40
Purchase #7	$62.55	9.848%	$68.7099	$68.71	$68.70	$68.70
7 purchase totals =	$503.37		$554.1856	$554.18	$554.10	$554.20