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	$137.28	4.375%	$143.286	$143.29	$143.30	$143.30
Purchase #2	$188.86	5.858%	$199.9234	$199.92	$199.90	$199.90
Purchase #3	$38.79	11.448%	$43.2307	$43.23	$43.25	$43.20
Purchase #4	$89.98	5.630%	$95.0459	$95.05	$95.05	$95.00
Purchase #5	$198.25	8.700%	$215.4978	$215.50	$215.50	$215.50
Purchase #6	$141.76	7.468%	$152.3466	$152.35	$152.35	$152.30
Purchase #7	$128.38	10.618%	$142.0114	$142.01	$142.00	$142.00
7 purchase totals =	$923.30		$991.3418	$991.35	$991.35	$991.20