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	$33.30	12.618%	$37.5018	$37.50	$37.50	$37.50
Purchase #2	$36.63	4.632%	$38.3267	$38.33	$38.35	$38.30
Purchase #3	$58.56	8.702%	$63.6559	$63.66	$63.65	$63.70
Purchase #4	$167.93	12.378%	$188.7164	$188.72	$188.70	$188.70
Purchase #5	$240.54	10.366%	$265.4744	$265.47	$265.45	$265.50
Purchase #6	$185.71	5.179%	$195.3279	$195.33	$195.35	$195.30
Purchase #7	$64.42	5.322%	$67.8484	$67.85	$67.85	$67.80
7 purchase totals =	$787.09		$856.8515	$856.86	$856.85	$856.80