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	$206.31	7.826%	$222.4558	$222.46	$222.45	$222.50
Purchase #2	$120.58	12.847%	$136.0709	$136.07	$136.05	$136.10
Purchase #3	$38.60	9.426%	$42.2384	$42.24	$42.25	$42.20
Purchase #4	$245.71	7.645%	$264.4945	$264.49	$264.50	$264.50
Purchase #5	$31.87	3.212%	$32.8937	$32.89	$32.90	$32.90
Purchase #6	$93.93	3.315%	$97.0438	$97.04	$97.05	$97.00
Purchase #7	$106.72	7.197%	$114.4006	$114.40	$114.40	$114.40
7 purchase totals =	$843.72		$909.5977	$909.59	$909.60	$909.60