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	$20.57	4.668%	$21.5302	$21.53	$21.55	$21.50
Purchase #2	$210.83	13.581%	$239.4628	$239.46	$239.45	$239.50
Purchase #3	$242.42	3.280%	$250.3714	$250.37	$250.35	$250.40
Purchase #4	$186.28	5.694%	$196.8868	$196.89	$196.90	$196.90
Purchase #5	$32.38	4.673%	$33.8931	$33.89	$33.90	$33.90
Purchase #6	$241.48	3.758%	$250.5548	$250.55	$250.55	$250.60
Purchase #7	$83.37	7.454%	$89.5844	$89.58	$89.60	$89.60
7 purchase totals =	$1,017.33		$1,082.2835	$1,082.27	$1,082.30	$1,082.40