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	$99.33	13.601%	$112.8399	$112.84	$112.85	$112.80
Purchase #2	$140.48	11.780%	$157.0285	$157.03	$157.05	$157.00
Purchase #3	$169.44	9.481%	$185.5046	$185.50	$185.50	$185.50
Purchase #4	$101.61	6.853%	$108.5733	$108.57	$108.55	$108.60
Purchase #5	$139.78	7.418%	$150.1489	$150.15	$150.15	$150.10
Purchase #6	$180.71	6.575%	$192.5917	$192.59	$192.60	$192.60
Purchase #7	$59.63	13.253%	$67.5328	$67.53	$67.55	$67.50
7 purchase totals =	$890.98		$974.2197	$974.21	$974.25	$974.10