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	$73.80	9.453%	$80.7763	$80.78	$80.80	$80.80
Purchase #2	$68.25	13.443%	$77.4248	$77.42	$77.40	$77.40
Purchase #3	$114.48	7.829%	$123.4426	$123.44	$123.45	$123.40
Purchase #4	$139.74	10.509%	$154.4253	$154.43	$154.45	$154.40
Purchase #5	$227.36	7.111%	$243.5276	$243.53	$243.55	$243.50
Purchase #6	$85.32	11.402%	$95.0482	$95.05	$95.05	$95.00
Purchase #7	$171.79	8.790%	$186.8903	$186.89	$186.90	$186.90
7 purchase totals =	$880.74		$961.5351	$961.54	$961.60	$961.40