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	$5.79	7.818%	$6.2427	$6.24	$6.25	$6.20
Purchase #2	$10.87	6.166%	$11.5402	$11.54	$11.55	$11.50
Purchase #3	$228.72	11.417%	$254.833	$254.83	$254.85	$254.80
Purchase #4	$189.72	5.588%	$200.3216	$200.32	$200.30	$200.30
Purchase #5	$37.83	3.479%	$39.1461	$39.15	$39.15	$39.10
Purchase #6	$31.57	7.482%	$33.9321	$33.93	$33.95	$33.90
Purchase #7	$45.55	13.856%	$51.8614	$51.86	$51.85	$51.90
7 purchase totals =	$550.05		$597.8771	$597.87	$597.90	$597.70