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	$55.64	7.425%	$59.7713	$59.77	$59.75	$59.80
Purchase #2	$147.81	12.689%	$166.5656	$166.57	$166.55	$166.60
Purchase #3	$109.80	10.833%	$121.6946	$121.69	$121.70	$121.70
Purchase #4	$29.61	11.441%	$32.9977	$33.00	$33.00	$33.00
Purchase #5	$80.59	5.647%	$85.1409	$85.14	$85.15	$85.10
Purchase #6	$154.81	10.485%	$171.0418	$171.04	$171.05	$171.00
Purchase #7	$114.50	8.751%	$124.5199	$124.52	$124.50	$124.50
7 purchase totals =	$692.76		$761.7318	$761.73	$761.70	$761.70