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	$245.50	12.708%	$276.6981	$276.70	$276.70	$276.70
Purchase #2	$30.25	7.540%	$32.5309	$32.53	$32.55	$32.50
Purchase #3	$178.31	6.471%	$189.8484	$189.85	$189.85	$189.80
Purchase #4	$37.36	7.632%	$40.2113	$40.21	$40.20	$40.20
Purchase #5	$82.66	3.184%	$85.2919	$85.29	$85.30	$85.30
Purchase #6	$156.31	7.719%	$168.3756	$168.38	$168.40	$168.40
Purchase #7	$166.68	9.435%	$182.4063	$182.41	$182.40	$182.40
7 purchase totals =	$897.07		$975.3625	$975.37	$975.40	$975.30