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	$22.61	12.576%	$25.4534	$25.45	$25.45	$25.50
Purchase #2	$8.54	3.128%	$8.8071	$8.81	$8.80	$8.80
Purchase #3	$17.86	6.284%	$18.9823	$18.98	$19.00	$19.00
Purchase #4	$168.48	12.154%	$188.9571	$188.96	$188.95	$189.00
Purchase #5	$40.31	4.717%	$42.2114	$42.21	$42.20	$42.20
Purchase #6	$91.94	9.347%	$100.5336	$100.53	$100.55	$100.50
Purchase #7	$101.98	12.319%	$114.5429	$114.54	$114.55	$114.50
7 purchase totals =	$451.72		$499.4878	$499.48	$499.50	$499.50