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	$52.80	12.300%	$59.2944	$59.29	$59.30	$59.30
Purchase #2	$91.34	8.471%	$99.0774	$99.08	$99.10	$99.10
Purchase #3	$241.35	10.718%	$267.2179	$267.22	$267.20	$267.20
Purchase #4	$178.39	10.412%	$196.964	$196.96	$196.95	$197.00
Purchase #5	$236.84	9.516%	$259.3777	$259.38	$259.40	$259.40
Purchase #6	$222.81	11.821%	$249.1484	$249.15	$249.15	$249.10
Purchase #7	$131.55	5.523%	$138.8155	$138.82	$138.80	$138.80
7 purchase totals =	$1,155.08		$1,269.8953	$1,269.90	$1,269.90	$1,269.90