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	$104.53	6.636%	$111.4666	$111.47	$111.45	$111.50
Purchase #2	$35.53	12.850%	$40.0956	$40.10	$40.10	$40.10
Purchase #3	$160.33	6.718%	$171.101	$171.10	$171.10	$171.10
Purchase #4	$223.77	11.725%	$250.007	$250.01	$250.00	$250.00
Purchase #5	$135.90	8.737%	$147.7736	$147.77	$147.75	$147.80
Purchase #6	$102.85	8.745%	$111.8442	$111.84	$111.85	$111.80
Purchase #7	$84.29	4.368%	$87.9718	$87.97	$87.95	$88.00
7 purchase totals =	$847.20		$920.2598	$920.26	$920.20	$920.30