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	$7.36	7.340%	$7.9002	$7.90	$7.90	$7.90
Purchase #2	$202.96	12.184%	$227.6886	$227.69	$227.70	$227.70
Purchase #3	$196.31	4.847%	$205.8251	$205.83	$205.85	$205.80
Purchase #4	$46.37	11.571%	$51.7355	$51.74	$51.75	$51.70
Purchase #5	$81.95	9.104%	$89.4107	$89.41	$89.40	$89.40
Purchase #6	$27.59	3.734%	$28.6202	$28.62	$28.60	$28.60
Purchase #7	$46.30	8.553%	$50.26	$50.26	$50.25	$50.30
7 purchase totals =	$608.84		$661.4403	$661.45	$661.45	$661.40