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	$58.81	13.801%	$66.9264	$66.93	$66.95	$66.90
Purchase #2	$94.43	5.796%	$99.9032	$99.90	$99.90	$99.90
Purchase #3	$53.52	4.362%	$55.8545	$55.85	$55.85	$55.90
Purchase #4	$93.70	5.139%	$98.5152	$98.52	$98.50	$98.50
Purchase #5	$184.52	11.652%	$206.0203	$206.02	$206.00	$206.00
Purchase #6	$39.47	8.242%	$42.7231	$42.72	$42.70	$42.70
Purchase #7	$112.98	9.531%	$123.7481	$123.75	$123.75	$123.70
7 purchase totals =	$637.43		$693.6908	$693.69	$693.65	$693.60