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	$31.96	3.427%	$33.0553	$33.06	$33.05	$33.10
Purchase #2	$37.97	6.772%	$40.5413	$40.54	$40.55	$40.50
Purchase #3	$151.93	9.374%	$166.1719	$166.17	$166.15	$166.20
Purchase #4	$123.50	11.419%	$137.6025	$137.60	$137.60	$137.60
Purchase #5	$141.90	10.514%	$156.8194	$156.82	$156.80	$156.80
Purchase #6	$99.48	11.538%	$110.958	$110.96	$110.95	$111.00
Purchase #7	$188.67	5.819%	$199.6487	$199.65	$199.65	$199.60
7 purchase totals =	$775.41		$844.7971	$844.80	$844.75	$844.80