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	$24.57	12.309%	$27.5943	$27.59	$27.60	$27.60
Purchase #2	$106.51	4.483%	$111.2848	$111.28	$111.30	$111.30
Purchase #3	$216.94	13.199%	$245.5739	$245.57	$245.55	$245.60
Purchase #4	$42.43	4.421%	$44.3058	$44.31	$44.30	$44.30
Purchase #5	$134.50	11.630%	$150.1424	$150.14	$150.15	$150.10
Purchase #6	$94.62	7.360%	$101.584	$101.58	$101.60	$101.60
Purchase #7	$5.30	5.652%	$5.5996	$5.60	$5.60	$5.60
7 purchase totals =	$624.87		$686.0848	$686.07	$686.10	$686.10