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	$34.88	8.437%	$37.8228	$37.82	$37.80	$37.80
Purchase #2	$215.71	13.758%	$245.3874	$245.39	$245.40	$245.40
Purchase #3	$32.89	13.721%	$37.4028	$37.40	$37.40	$37.40
Purchase #4	$246.38	5.311%	$259.4652	$259.47	$259.45	$259.50
Purchase #5	$43.28	10.718%	$47.9188	$47.92	$47.90	$47.90
Purchase #6	$58.99	13.766%	$67.1106	$67.11	$67.10	$67.10
Purchase #7	$85.69	8.279%	$92.7843	$92.78	$92.80	$92.80
7 purchase totals =	$717.82		$787.8919	$787.89	$787.85	$787.90