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	$126.82	10.249%	$139.8178	$139.82	$139.80	$139.80
Purchase #2	$199.72	10.311%	$220.3131	$220.31	$220.30	$220.30
Purchase #3	$8.40	13.590%	$9.5416	$9.54	$9.55	$9.50
Purchase #4	$56.89	12.261%	$63.8653	$63.87	$63.85	$63.90
Purchase #5	$249.86	6.220%	$265.4013	$265.40	$265.40	$265.40
Purchase #6	$40.91	6.272%	$43.4759	$43.48	$43.50	$43.50
Purchase #7	$143.74	4.705%	$150.503	$150.50	$150.50	$150.50
7 purchase totals =	$826.34		$892.9180	$892.92	$892.90	$892.90