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	$189.73	13.488%	$215.3208	$215.32	$215.30	$215.30
Purchase #2	$221.61	13.429%	$251.37	$251.37	$251.35	$251.40
Purchase #3	$211.72	8.861%	$230.4805	$230.48	$230.50	$230.50
Purchase #4	$71.68	6.518%	$76.3521	$76.35	$76.35	$76.40
Purchase #5	$150.40	11.348%	$167.4674	$167.47	$167.45	$167.50
Purchase #6	$197.94	10.280%	$218.2882	$218.29	$218.30	$218.30
Purchase #7	$29.57	9.789%	$32.4646	$32.46	$32.45	$32.50
7 purchase totals =	$1,072.65		$1,191.7436	$1,191.74	$1,191.70	$1,191.90