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	$73.73	9.121%	$80.4549	$80.45	$80.45	$80.50
Purchase #2	$36.84	5.382%	$38.8227	$38.82	$38.80	$38.80
Purchase #3	$98.67	11.302%	$109.8217	$109.82	$109.80	$109.80
Purchase #4	$26.34	4.420%	$27.5042	$27.50	$27.50	$27.50
Purchase #5	$50.82	10.204%	$56.0057	$56.01	$56.00	$56.00
Purchase #6	$88.41	8.540%	$95.9602	$95.96	$95.95	$96.00
Purchase #7	$175.33	9.193%	$191.4481	$191.45	$191.45	$191.40
7 purchase totals =	$550.14		$600.0175	$600.01	$599.95	$600.00