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	$184.61	8.770%	$200.8003	$200.80	$200.80	$200.80
Purchase #2	$33.98	13.188%	$38.4613	$38.46	$38.45	$38.50
Purchase #3	$38.57	10.478%	$42.6114	$42.61	$42.60	$42.60
Purchase #4	$34.32	6.659%	$36.6054	$36.61	$36.60	$36.60
Purchase #5	$246.59	9.872%	$270.9334	$270.93	$270.95	$270.90
Purchase #6	$90.76	6.666%	$96.8101	$96.81	$96.80	$96.80
Purchase #7	$94.50	7.628%	$101.7085	$101.71	$101.70	$101.70
7 purchase totals =	$723.33		$787.9304	$787.93	$787.90	$787.90