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	$19.48	3.228%	$20.1088	$20.11	$20.10	$20.10
Purchase #2	$64.81	3.290%	$66.9422	$66.94	$66.95	$66.90
Purchase #3	$151.67	13.356%	$171.927	$171.93	$171.95	$171.90
Purchase #4	$55.86	8.268%	$60.4785	$60.48	$60.50	$60.50
Purchase #5	$82.71	8.698%	$89.9041	$89.90	$89.90	$89.90
Purchase #6	$78.97	8.308%	$85.5308	$85.53	$85.55	$85.50
Purchase #7	$225.73	12.731%	$254.4677	$254.47	$254.45	$254.50
7 purchase totals =	$679.23		$749.3591	$749.36	$749.40	$749.30