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	$121.38	10.375%	$133.9732	$133.97	$133.95	$134.00
Purchase #2	$219.35	5.543%	$231.5086	$231.51	$231.50	$231.50
Purchase #3	$42.50	12.681%	$47.8894	$47.89	$47.90	$47.90
Purchase #4	$109.92	8.107%	$118.8312	$118.83	$118.85	$118.80
Purchase #5	$41.84	4.722%	$43.8157	$43.82	$43.80	$43.80
Purchase #6	$177.97	10.267%	$196.2422	$196.24	$196.25	$196.20
Purchase #7	$71.40	8.791%	$77.6768	$77.68	$77.70	$77.70
7 purchase totals =	$784.36		$849.9371	$849.94	$849.95	$849.90