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	$249.92	9.709%	$274.1847	$274.18	$274.20	$274.20
Purchase #2	$45.59	11.447%	$50.8087	$50.81	$50.80	$50.80
Purchase #3	$208.39	12.401%	$234.2324	$234.23	$234.25	$234.20
Purchase #4	$75.41	3.566%	$78.0991	$78.10	$78.10	$78.10
Purchase #5	$247.27	12.534%	$278.2628	$278.26	$278.25	$278.30
Purchase #6	$17.81	12.555%	$20.046	$20.05	$20.05	$20.00
Purchase #7	$101.34	8.436%	$109.889	$109.89	$109.90	$109.90
7 purchase totals =	$945.73		$1,045.5227	$1,045.52	$1,045.55	$1,045.50