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	$250.78	7.779%	$270.2882	$270.29	$270.30	$270.30
Purchase #2	$163.25	11.317%	$181.725	$181.73	$181.75	$181.70
Purchase #3	$135.89	3.417%	$140.5334	$140.53	$140.55	$140.50
Purchase #4	$180.55	8.595%	$196.0683	$196.07	$196.05	$196.10
Purchase #5	$159.77	3.792%	$165.8285	$165.83	$165.85	$165.80
Purchase #6	$240.51	6.805%	$256.8767	$256.88	$256.90	$256.90
Purchase #7	$14.40	9.425%	$15.7572	$15.76	$15.75	$15.80
7 purchase totals =	$1,145.15		$1,227.0773	$1,227.09	$1,227.15	$1,227.10