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	$112.49	7.285%	$120.6849	$120.68	$120.70	$120.70
Purchase #2	$104.81	10.400%	$115.7102	$115.71	$115.70	$115.70
Purchase #3	$55.45	7.369%	$59.5361	$59.54	$59.55	$59.50
Purchase #4	$128.33	8.179%	$138.8261	$138.83	$138.85	$138.80
Purchase #5	$189.78	5.459%	$200.1401	$200.14	$200.15	$200.10
Purchase #6	$89.48	4.386%	$93.4046	$93.40	$93.40	$93.40
Purchase #7	$68.88	13.614%	$78.2573	$78.26	$78.25	$78.30
7 purchase totals =	$749.22		$806.5593	$806.56	$806.60	$806.50