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	$50.45	12.682%	$56.8481	$56.85	$56.85	$56.80
Purchase #2	$31.88	6.354%	$33.9057	$33.91	$33.90	$33.90
Purchase #3	$142.53	11.614%	$159.0834	$159.08	$159.10	$159.10
Purchase #4	$154.71	8.170%	$167.3498	$167.35	$167.35	$167.30
Purchase #5	$134.37	12.332%	$150.9405	$150.94	$150.95	$150.90
Purchase #6	$208.30	6.301%	$221.425	$221.43	$221.45	$221.40
Purchase #7	$94.31	6.565%	$100.5015	$100.50	$100.50	$100.50
7 purchase totals =	$816.55		$890.0540	$890.06	$890.10	$889.90