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	$29.31	7.495%	$31.5068	$31.51	$31.50	$31.50
Purchase #2	$76.50	9.605%	$83.8478	$83.85	$83.85	$83.80
Purchase #3	$93.31	12.481%	$104.956	$104.96	$104.95	$105.00
Purchase #4	$32.43	6.473%	$34.5292	$34.53	$34.55	$34.50
Purchase #5	$43.66	8.801%	$47.5025	$47.50	$47.50	$47.50
Purchase #6	$128.91	6.732%	$137.5882	$137.59	$137.60	$137.60
Purchase #7	$231.80	5.819%	$245.2884	$245.29	$245.30	$245.30
7 purchase totals =	$635.92		$685.2189	$685.23	$685.25	$685.20