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	$115.88	7.721%	$124.8271	$124.83	$124.85	$124.80
Purchase #2	$148.48	13.340%	$168.2872	$168.29	$168.30	$168.30
Purchase #3	$139.43	6.460%	$148.4372	$148.44	$148.45	$148.40
Purchase #4	$130.86	6.249%	$139.0374	$139.04	$139.05	$139.00
Purchase #5	$73.32	6.344%	$77.9714	$77.97	$77.95	$78.00
Purchase #6	$78.47	8.642%	$85.2514	$85.25	$85.25	$85.30
Purchase #7	$41.91	4.118%	$43.6359	$43.64	$43.65	$43.60
7 purchase totals =	$728.35		$787.4476	$787.46	$787.50	$787.40