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	$73.80	6.300%	$78.4494	$78.45	$78.45	$78.40
Purchase #2	$216.33	9.767%	$237.459	$237.46	$237.45	$237.50
Purchase #3	$190.57	8.297%	$206.3816	$206.38	$206.40	$206.40
Purchase #4	$172.35	10.776%	$190.9224	$190.92	$190.90	$190.90
Purchase #5	$81.82	4.392%	$85.4135	$85.41	$85.40	$85.40
Purchase #6	$79.27	11.752%	$88.5858	$88.59	$88.60	$88.60
Purchase #7	$27.93	13.201%	$31.617	$31.62	$31.60	$31.60
7 purchase totals =	$842.07		$918.8287	$918.83	$918.80	$918.80