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	$66.50	10.283%	$73.3382	$73.34	$73.35	$73.30
Purchase #2	$86.67	11.741%	$96.8459	$96.85	$96.85	$96.80
Purchase #3	$153.96	4.300%	$160.5803	$160.58	$160.60	$160.60
Purchase #4	$248.77	13.302%	$281.8614	$281.86	$281.85	$281.90
Purchase #5	$50.58	3.651%	$52.4267	$52.43	$52.45	$52.40
Purchase #6	$182.70	8.533%	$198.2898	$198.29	$198.30	$198.30
Purchase #7	$135.98	4.350%	$141.8951	$141.90	$141.90	$141.90
7 purchase totals =	$925.16		$1,005.2374	$1,005.25	$1,005.30	$1,005.20