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	$54.88	11.734%	$61.3196	$61.32	$61.30	$61.30
Purchase #2	$113.46	9.148%	$123.8393	$123.84	$123.85	$123.80
Purchase #3	$226.42	13.274%	$256.475	$256.48	$256.50	$256.50
Purchase #4	$122.28	9.367%	$133.734	$133.73	$133.75	$133.70
Purchase #5	$70.62	10.598%	$78.1043	$78.10	$78.10	$78.10
Purchase #6	$128.25	7.457%	$137.8136	$137.81	$137.80	$137.80
Purchase #7	$54.81	5.726%	$57.9484	$57.95	$57.95	$57.90
7 purchase totals =	$770.72		$849.2342	$849.23	$849.25	$849.10