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	$244.44	10.157%	$269.2678	$269.27	$269.25	$269.30
Purchase #2	$122.92	8.598%	$133.4887	$133.49	$133.50	$133.50
Purchase #3	$222.63	12.695%	$250.8929	$250.89	$250.90	$250.90
Purchase #4	$208.86	10.712%	$231.2331	$231.23	$231.25	$231.20
Purchase #5	$65.54	8.803%	$71.3095	$71.31	$71.30	$71.30
Purchase #6	$139.90	6.387%	$148.8354	$148.84	$148.85	$148.80
Purchase #7	$186.31	5.364%	$196.3037	$196.30	$196.30	$196.30
7 purchase totals =	$1,190.60		$1,301.3311	$1,301.33	$1,301.35	$1,301.30