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	$63.32	12.729%	$71.38	$71.38	$71.40	$71.40
Purchase #2	$141.62	13.601%	$160.8817	$160.88	$160.90	$160.90
Purchase #3	$92.85	10.132%	$102.2576	$102.26	$102.25	$102.30
Purchase #4	$144.88	13.248%	$164.0737	$164.07	$164.05	$164.10
Purchase #5	$68.66	4.109%	$71.4812	$71.48	$71.50	$71.50
Purchase #6	$132.96	9.401%	$145.4596	$145.46	$145.45	$145.50
Purchase #7	$238.36	7.807%	$256.9688	$256.97	$256.95	$257.00
7 purchase totals =	$882.65		$972.5026	$972.50	$972.50	$972.70