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	$79.80	13.757%	$90.7781	$90.78	$90.80	$90.80
Purchase #2	$199.35	11.601%	$222.4766	$222.48	$222.50	$222.50
Purchase #3	$114.37	9.433%	$125.1585	$125.16	$125.15	$125.20
Purchase #4	$191.94	13.298%	$217.4642	$217.46	$217.45	$217.50
Purchase #5	$140.33	11.595%	$156.6013	$156.60	$156.60	$156.60
Purchase #6	$57.64	5.841%	$61.0068	$61.01	$61.00	$61.00
Purchase #7	$202.86	12.401%	$228.0167	$228.02	$228.00	$228.00
7 purchase totals =	$986.29		$1,101.5022	$1,101.51	$1,101.50	$1,101.60