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	$93.78	7.146%	$100.4815	$100.48	$100.50	$100.50
Purchase #2	$246.88	9.247%	$269.709	$269.71	$269.70	$269.70
Purchase #3	$147.39	5.742%	$155.8531	$155.85	$155.85	$155.90
Purchase #4	$245.96	6.443%	$261.8072	$261.81	$261.80	$261.80
Purchase #5	$22.37	12.188%	$25.0965	$25.10	$25.10	$25.10
Purchase #6	$99.71	5.182%	$104.877	$104.88	$104.90	$104.90
Purchase #7	$55.92	13.212%	$63.3082	$63.31	$63.30	$63.30
7 purchase totals =	$912.01		$981.1325	$981.14	$981.15	$981.20