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	$218.78	10.571%	$241.9072	$241.91	$241.90	$241.90
Purchase #2	$108.95	7.857%	$117.5102	$117.51	$117.50	$117.50
Purchase #3	$129.61	8.386%	$140.4791	$140.48	$140.50	$140.50
Purchase #4	$122.34	7.825%	$131.9131	$131.91	$131.90	$131.90
Purchase #5	$42.77	4.453%	$44.6745	$44.67	$44.65	$44.70
Purchase #6	$245.67	9.142%	$268.1292	$268.13	$268.15	$268.10
Purchase #7	$66.27	7.655%	$71.343	$71.34	$71.35	$71.30
7 purchase totals =	$934.39		$1,015.9563	$1,015.95	$1,015.95	$1,015.90