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	$70.83	9.111%	$77.2833	$77.28	$77.30	$77.30
Purchase #2	$199.95	4.469%	$208.8858	$208.89	$208.90	$208.90
Purchase #3	$36.57	11.553%	$40.7949	$40.79	$40.80	$40.80
Purchase #4	$33.86	7.533%	$36.4107	$36.41	$36.40	$36.40
Purchase #5	$179.31	9.214%	$195.8316	$195.83	$195.85	$195.80
Purchase #6	$117.93	9.143%	$128.7123	$128.71	$128.70	$128.70
Purchase #7	$82.48	12.165%	$92.5137	$92.51	$92.50	$92.50
7 purchase totals =	$720.93		$780.4323	$780.42	$780.45	$780.40