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	$120.94	6.279%	$128.5338	$128.53	$128.55	$128.50
Purchase #2	$234.57	9.544%	$256.9574	$256.96	$256.95	$257.00
Purchase #3	$40.82	6.601%	$43.5145	$43.51	$43.50	$43.50
Purchase #4	$83.33	3.503%	$86.249	$86.25	$86.25	$86.20
Purchase #5	$123.97	8.261%	$134.2112	$134.21	$134.20	$134.20
Purchase #6	$94.48	11.336%	$105.1903	$105.19	$105.20	$105.20
Purchase #7	$37.99	7.710%	$40.919	$40.92	$40.90	$40.90
7 purchase totals =	$736.10		$795.5752	$795.57	$795.55	$795.50