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	$29.26	7.269%	$31.3869	$31.39	$31.40	$31.40
Purchase #2	$31.54	7.489%	$33.902	$33.90	$33.90	$33.90
Purchase #3	$190.47	9.655%	$208.8599	$208.86	$208.85	$208.90
Purchase #4	$37.72	5.287%	$39.7143	$39.71	$39.70	$39.70
Purchase #5	$82.80	4.725%	$86.7123	$86.71	$86.70	$86.70
Purchase #6	$154.79	9.434%	$169.3929	$169.39	$169.40	$169.40
Purchase #7	$103.91	5.814%	$109.9513	$109.95	$109.95	$110.00
7 purchase totals =	$630.49		$679.9196	$679.91	$679.90	$680.00