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	$36.70	7.627%	$39.4991	$39.50	$39.50	$39.50
Purchase #2	$147.33	9.644%	$161.5385	$161.54	$161.55	$161.50
Purchase #3	$72.85	7.602%	$78.3881	$78.39	$78.40	$78.40
Purchase #4	$161.52	11.120%	$179.481	$179.48	$179.50	$179.50
Purchase #5	$245.40	10.391%	$270.8995	$270.90	$270.90	$270.90
Purchase #6	$91.73	12.827%	$103.4962	$103.50	$103.50	$103.50
Purchase #7	$35.78	13.131%	$40.4783	$40.48	$40.50	$40.50
7 purchase totals =	$791.31		$873.7807	$873.79	$873.85	$873.80