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	$93.39	6.576%	$99.5313	$99.53	$99.55	$99.50
Purchase #2	$47.44	8.538%	$51.4904	$51.49	$51.50	$51.50
Purchase #3	$196.61	6.712%	$209.8065	$209.81	$209.80	$209.80
Purchase #4	$75.49	11.614%	$84.2574	$84.26	$84.25	$84.30
Purchase #5	$239.50	5.176%	$251.8965	$251.90	$251.90	$251.90
Purchase #6	$99.83	5.589%	$105.4095	$105.41	$105.40	$105.40
Purchase #7	$225.89	12.564%	$254.2708	$254.27	$254.25	$254.30
7 purchase totals =	$978.15		$1,056.6624	$1,056.67	$1,056.65	$1,056.70