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	$28.26	12.245%	$31.7204	$31.72	$31.70	$31.70
Purchase #2	$160.51	13.830%	$182.7085	$182.71	$182.70	$182.70
Purchase #3	$143.96	10.772%	$159.4674	$159.47	$159.45	$159.50
Purchase #4	$161.91	7.488%	$174.0338	$174.03	$174.05	$174.00
Purchase #5	$75.93	13.805%	$86.4121	$86.41	$86.40	$86.40
Purchase #6	$27.73	13.601%	$31.5016	$31.50	$31.50	$31.50
Purchase #7	$226.27	13.162%	$256.0517	$256.05	$256.05	$256.10
7 purchase totals =	$824.57		$921.8955	$921.89	$921.85	$921.90