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	$121.82	7.483%	$130.9358	$130.94	$130.95	$130.90
Purchase #2	$45.70	13.775%	$51.9952	$52.00	$52.00	$52.00
Purchase #3	$191.86	7.794%	$206.8136	$206.81	$206.80	$206.80
Purchase #4	$182.39	3.681%	$189.1038	$189.10	$189.10	$189.10
Purchase #5	$86.28	12.789%	$97.3143	$97.31	$97.30	$97.30
Purchase #6	$134.48	7.463%	$144.5162	$144.52	$144.50	$144.50
Purchase #7	$91.39	10.350%	$100.8489	$100.85	$100.85	$100.80
7 purchase totals =	$853.92		$921.5278	$921.53	$921.50	$921.40