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	$230.61	12.574%	$259.6069	$259.61	$259.60	$259.60
Purchase #2	$187.39	6.589%	$199.7371	$199.74	$199.75	$199.70
Purchase #3	$143.76	11.508%	$160.3039	$160.30	$160.30	$160.30
Purchase #4	$158.83	5.677%	$167.8468	$167.85	$167.85	$167.80
Purchase #5	$76.84	5.315%	$80.924	$80.92	$80.90	$80.90
Purchase #6	$67.92	12.721%	$76.5601	$76.56	$76.55	$76.60
Purchase #7	$183.25	7.165%	$196.3799	$196.38	$196.40	$196.40
7 purchase totals =	$1,048.60		$1,141.3587	$1,141.36	$1,141.35	$1,141.30