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	$83.30	8.668%	$90.5204	$90.52	$90.50	$90.50
Purchase #2	$227.67	9.848%	$250.0909	$250.09	$250.10	$250.10
Purchase #3	$45.45	8.562%	$49.3414	$49.34	$49.35	$49.30
Purchase #4	$69.32	12.830%	$78.2138	$78.21	$78.20	$78.20
Purchase #5	$243.58	4.168%	$253.7324	$253.73	$253.75	$253.70
Purchase #6	$218.67	9.354%	$239.1244	$239.12	$239.10	$239.10
Purchase #7	$68.35	6.102%	$72.5207	$72.52	$72.50	$72.50
7 purchase totals =	$956.34		$1,033.5440	$1,033.53	$1,033.50	$1,033.40