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	$144.86	4.337%	$151.1426	$151.14	$151.15	$151.10
Purchase #2	$244.93	12.157%	$274.7061	$274.71	$274.70	$274.70
Purchase #3	$183.72	11.465%	$204.7835	$204.78	$204.80	$204.80
Purchase #4	$169.83	12.752%	$191.4867	$191.49	$191.50	$191.50
Purchase #5	$22.71	5.749%	$24.0156	$24.02	$24.00	$24.00
Purchase #6	$75.68	13.641%	$86.0035	$86.00	$86.00	$86.00
Purchase #7	$79.81	13.774%	$90.803	$90.80	$90.80	$90.80
7 purchase totals =	$921.54		$1,022.9410	$1,022.94	$1,022.95	$1,022.90