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	$74.27	4.285%	$77.4525	$77.45	$77.45	$77.50
Purchase #2	$99.46	8.813%	$108.2254	$108.23	$108.25	$108.20
Purchase #3	$32.62	8.867%	$35.5124	$35.51	$35.50	$35.50
Purchase #4	$40.36	7.715%	$43.4738	$43.47	$43.45	$43.50
Purchase #5	$85.57	5.736%	$90.4783	$90.48	$90.50	$90.50
Purchase #6	$39.46	11.519%	$44.0054	$44.01	$44.00	$44.00
Purchase #7	$32.88	13.745%	$37.3994	$37.40	$37.40	$37.40
7 purchase totals =	$404.62		$436.5472	$436.55	$436.55	$436.60