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	$82.78	9.654%	$90.7716	$90.77	$90.75	$90.80
Purchase #2	$197.50	3.743%	$204.8924	$204.89	$204.90	$204.90
Purchase #3	$115.76	13.798%	$131.7326	$131.73	$131.75	$131.70
Purchase #4	$163.29	10.408%	$180.2852	$180.29	$180.30	$180.30
Purchase #5	$63.67	6.496%	$67.806	$67.81	$67.80	$67.80
Purchase #6	$98.43	11.669%	$109.9158	$109.92	$109.90	$109.90
Purchase #7	$212.94	5.317%	$224.262	$224.26	$224.25	$224.30
7 purchase totals =	$934.37		$1,009.6656	$1,009.67	$1,009.65	$1,009.70