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	$37.97	12.476%	$42.7071	$42.71	$42.70	$42.70
Purchase #2	$205.64	6.181%	$218.3506	$218.35	$218.35	$218.40
Purchase #3	$147.35	3.701%	$152.8034	$152.80	$152.80	$152.80
Purchase #4	$181.75	8.133%	$196.5317	$196.53	$196.55	$196.50
Purchase #5	$79.96	4.483%	$83.5446	$83.54	$83.55	$83.50
Purchase #6	$43.61	8.866%	$47.4765	$47.48	$47.50	$47.50
Purchase #7	$33.66	10.848%	$37.3114	$37.31	$37.30	$37.30
7 purchase totals =	$729.94		$778.7253	$778.72	$778.75	$778.70