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	$27.77	13.131%	$31.4165	$31.42	$31.40	$31.40
Purchase #2	$53.81	3.336%	$55.6051	$55.61	$55.60	$55.60
Purchase #3	$170.73	5.617%	$180.3199	$180.32	$180.30	$180.30
Purchase #4	$247.82	9.717%	$271.9007	$271.90	$271.90	$271.90
Purchase #5	$194.69	7.145%	$208.6006	$208.60	$208.60	$208.60
Purchase #6	$188.76	10.570%	$208.7119	$208.71	$208.70	$208.70
Purchase #7	$6.42	13.443%	$7.283	$7.28	$7.30	$7.30
7 purchase totals =	$890.00		$963.8377	$963.84	$963.80	$963.80