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	$166.74	6.653%	$177.8332	$177.83	$177.85	$177.80
Purchase #2	$184.31	6.797%	$196.8376	$196.84	$196.85	$196.80
Purchase #3	$82.99	5.705%	$87.7246	$87.72	$87.70	$87.70
Purchase #4	$125.58	4.799%	$131.6066	$131.61	$131.60	$131.60
Purchase #5	$82.33	4.682%	$86.1847	$86.18	$86.20	$86.20
Purchase #6	$85.57	4.840%	$89.7116	$89.71	$89.70	$89.70
Purchase #7	$18.54	6.344%	$19.7162	$19.72	$19.70	$19.70
7 purchase totals =	$746.06		$789.6145	$789.61	$789.60	$789.50