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	$53.75	8.525%	$58.3322	$58.33	$58.35	$58.30
Purchase #2	$155.61	6.871%	$166.302	$166.30	$166.30	$166.30
Purchase #3	$30.54	6.646%	$32.5697	$32.57	$32.55	$32.60
Purchase #4	$185.36	3.403%	$191.6678	$191.67	$191.65	$191.70
Purchase #5	$52.88	12.747%	$59.6206	$59.62	$59.60	$59.60
Purchase #6	$234.37	10.725%	$259.5062	$259.51	$259.50	$259.50
Purchase #7	$207.86	8.700%	$225.9438	$225.94	$225.95	$225.90
7 purchase totals =	$920.37		$993.9423	$993.94	$993.90	$993.90