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	$136.25	7.818%	$146.902	$146.90	$146.90	$146.90
Purchase #2	$157.85	13.335%	$178.8993	$178.90	$178.90	$178.90
Purchase #3	$106.60	5.484%	$112.4459	$112.45	$112.45	$112.40
Purchase #4	$84.90	5.786%	$89.8123	$89.81	$89.80	$89.80
Purchase #5	$98.27	8.111%	$106.2407	$106.24	$106.25	$106.20
Purchase #6	$42.60	11.566%	$47.5271	$47.53	$47.55	$47.50
Purchase #7	$180.46	10.837%	$200.0165	$200.02	$200.00	$200.00
7 purchase totals =	$806.93		$881.8438	$881.85	$881.85	$881.70