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	$242.62	13.613%	$275.6479	$275.65	$275.65	$275.60
Purchase #2	$91.35	9.360%	$99.9004	$99.90	$99.90	$99.90
Purchase #3	$92.95	12.409%	$104.4842	$104.48	$104.50	$104.50
Purchase #4	$7.64	9.502%	$8.366	$8.37	$8.35	$8.40
Purchase #5	$36.79	4.143%	$38.3142	$38.31	$38.30	$38.30
Purchase #6	$59.96	7.683%	$64.5667	$64.57	$64.55	$64.60
Purchase #7	$239.39	3.675%	$248.1876	$248.19	$248.20	$248.20
7 purchase totals =	$770.70		$839.4670	$839.47	$839.45	$839.50