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	$99.55	13.612%	$113.1007	$113.10	$113.10	$113.10
Purchase #2	$110.72	10.471%	$122.3135	$122.31	$122.30	$122.30
Purchase #3	$224.78	7.445%	$241.5149	$241.51	$241.50	$241.50
Purchase #4	$44.98	4.818%	$47.1471	$47.15	$47.15	$47.10
Purchase #5	$82.80	3.736%	$85.8934	$85.89	$85.90	$85.90
Purchase #6	$89.88	11.691%	$100.3879	$100.39	$100.40	$100.40
Purchase #7	$132.34	6.119%	$140.4379	$140.44	$140.45	$140.40
7 purchase totals =	$785.05		$850.7954	$850.79	$850.80	$850.70