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	$68.28	4.459%	$71.3246	$71.32	$71.30	$71.30
Purchase #2	$232.79	12.589%	$262.0959	$262.10	$262.10	$262.10
Purchase #3	$193.85	12.481%	$218.0444	$218.04	$218.05	$218.00
Purchase #4	$44.68	13.830%	$50.8592	$50.86	$50.85	$50.90
Purchase #5	$52.84	13.392%	$59.9163	$59.92	$59.90	$59.90
Purchase #6	$75.44	4.523%	$78.8522	$78.85	$78.85	$78.90
Purchase #7	$242.99	7.185%	$260.4488	$260.45	$260.45	$260.40
7 purchase totals =	$910.87		$1,001.5414	$1,001.54	$1,001.50	$1,001.50