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	$25.85	6.202%	$27.4532	$27.45	$27.45	$27.50
Purchase #2	$241.66	7.586%	$259.9923	$259.99	$260.00	$260.00
Purchase #3	$43.92	4.494%	$45.8938	$45.89	$45.90	$45.90
Purchase #4	$225.69	7.279%	$242.118	$242.12	$242.10	$242.10
Purchase #5	$142.89	8.555%	$155.1142	$155.11	$155.10	$155.10
Purchase #6	$55.82	9.813%	$61.2976	$61.30	$61.30	$61.30
Purchase #7	$196.50	12.312%	$220.6931	$220.69	$220.70	$220.70
7 purchase totals =	$932.33		$1,012.5622	$1,012.55	$1,012.55	$1,012.60