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	$247.97	11.657%	$276.8759	$276.88	$276.90	$276.90
Purchase #2	$209.38	7.747%	$225.6007	$225.60	$225.60	$225.60
Purchase #3	$113.98	8.549%	$123.7242	$123.72	$123.70	$123.70
Purchase #4	$29.72	13.403%	$33.7034	$33.70	$33.70	$33.70
Purchase #5	$161.96	7.264%	$173.7248	$173.72	$173.70	$173.70
Purchase #6	$77.85	11.507%	$86.8082	$86.81	$86.80	$86.80
Purchase #7	$73.97	11.716%	$82.6363	$82.64	$82.65	$82.60
7 purchase totals =	$914.83		$1,003.0735	$1,003.07	$1,003.05	$1,003.00