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	$74.75	9.850%	$82.1129	$82.11	$82.10	$82.10
Purchase #2	$34.32	10.281%	$37.8484	$37.85	$37.85	$37.80
Purchase #3	$41.26	7.581%	$44.3879	$44.39	$44.40	$44.40
Purchase #4	$141.77	10.175%	$156.1951	$156.20	$156.20	$156.20
Purchase #5	$166.30	11.482%	$185.3946	$185.39	$185.40	$185.40
Purchase #6	$67.40	12.588%	$75.8843	$75.88	$75.90	$75.90
Purchase #7	$226.64	6.294%	$240.9047	$240.90	$240.90	$240.90
7 purchase totals =	$752.44		$822.7279	$822.72	$822.75	$822.70