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	$228.27	6.539%	$243.1966	$243.20	$243.20	$243.20
Purchase #2	$7.58	4.223%	$7.9001	$7.90	$7.90	$7.90
Purchase #3	$84.83	6.291%	$90.1667	$90.17	$90.15	$90.20
Purchase #4	$45.48	12.465%	$51.1491	$51.15	$51.15	$51.10
Purchase #5	$169.44	9.465%	$185.4775	$185.48	$185.50	$185.50
Purchase #6	$137.80	9.630%	$151.0701	$151.07	$151.05	$151.10
Purchase #7	$233.58	3.266%	$241.2087	$241.21	$241.20	$241.20
7 purchase totals =	$906.98		$970.1688	$970.18	$970.15	$970.20