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	$135.29	12.423%	$152.0971	$152.10	$152.10	$152.10
Purchase #2	$29.91	12.862%	$33.757	$33.76	$33.75	$33.80
Purchase #3	$180.30	5.113%	$189.5187	$189.52	$189.50	$189.50
Purchase #4	$210.76	5.706%	$222.786	$222.79	$222.80	$222.80
Purchase #5	$170.43	8.777%	$185.3886	$185.39	$185.40	$185.40
Purchase #6	$131.26	8.507%	$142.4263	$142.43	$142.45	$142.40
Purchase #7	$67.92	7.501%	$73.0147	$73.01	$73.00	$73.00
7 purchase totals =	$925.87		$998.9884	$999.00	$999.00	$999.00