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	$47.40	6.696%	$50.5739	$50.57	$50.55	$50.60
Purchase #2	$184.62	11.847%	$206.4919	$206.49	$206.50	$206.50
Purchase #3	$73.95	6.121%	$78.4765	$78.48	$78.50	$78.50
Purchase #4	$162.67	3.609%	$168.5408	$168.54	$168.55	$168.50
Purchase #5	$33.44	11.801%	$37.3863	$37.39	$37.40	$37.40
Purchase #6	$84.60	10.568%	$93.5405	$93.54	$93.55	$93.50
Purchase #7	$9.88	9.832%	$10.8514	$10.85	$10.85	$10.90
7 purchase totals =	$596.56		$645.8613	$645.86	$645.90	$645.90