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	$131.78	9.626%	$144.4651	$144.47	$144.45	$144.50
Purchase #2	$232.67	12.811%	$262.4774	$262.48	$262.50	$262.50
Purchase #3	$85.71	12.541%	$96.4589	$96.46	$96.45	$96.50
Purchase #4	$57.78	8.355%	$62.6075	$62.61	$62.60	$62.60
Purchase #5	$144.89	12.315%	$162.7332	$162.73	$162.75	$162.70
Purchase #6	$152.60	4.365%	$159.261	$159.26	$159.25	$159.30
Purchase #7	$180.69	9.849%	$198.4862	$198.49	$198.50	$198.50
7 purchase totals =	$986.12		$1,086.4893	$1,086.50	$1,086.50	$1,086.60