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	$91.34	8.417%	$99.0281	$99.03	$99.05	$99.00
Purchase #2	$137.84	9.207%	$150.5309	$150.53	$150.55	$150.50
Purchase #3	$173.86	9.577%	$190.5106	$190.51	$190.50	$190.50
Purchase #4	$109.71	4.567%	$114.7205	$114.72	$114.70	$114.70
Purchase #5	$226.30	11.831%	$253.0736	$253.07	$253.05	$253.10
Purchase #6	$174.99	9.339%	$191.3323	$191.33	$191.35	$191.30
Purchase #7	$201.83	11.372%	$224.7821	$224.78	$224.80	$224.80
7 purchase totals =	$1,115.87		$1,223.9781	$1,223.97	$1,224.00	$1,223.90