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	$39.85	13.445%	$45.2078	$45.21	$45.20	$45.20
Purchase #2	$240.93	7.443%	$258.8624	$258.86	$258.85	$258.90
Purchase #3	$16.45	9.783%	$18.0593	$18.06	$18.05	$18.10
Purchase #4	$234.40	5.171%	$246.5208	$246.52	$246.50	$246.50
Purchase #5	$147.91	9.654%	$162.1892	$162.19	$162.20	$162.20
Purchase #6	$125.75	4.275%	$131.1258	$131.13	$131.15	$131.10
Purchase #7	$53.39	6.547%	$56.8854	$56.89	$56.90	$56.90
7 purchase totals =	$858.68		$918.8507	$918.86	$918.85	$918.90