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	$20.33	10.778%	$22.5212	$22.52	$22.50	$22.50
Purchase #2	$140.96	3.220%	$145.4989	$145.50	$145.50	$145.50
Purchase #3	$182.33	7.473%	$195.9555	$195.96	$195.95	$196.00
Purchase #4	$90.34	11.314%	$100.5611	$100.56	$100.55	$100.60
Purchase #5	$44.36	3.191%	$45.7755	$45.78	$45.80	$45.80
Purchase #6	$182.82	3.663%	$189.5167	$189.52	$189.50	$189.50
Purchase #7	$123.25	10.390%	$136.0557	$136.06	$136.05	$136.10
7 purchase totals =	$784.39		$835.8846	$835.90	$835.85	$836.00