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	$157.91	12.411%	$177.5082	$177.51	$177.50	$177.50
Purchase #2	$250.33	9.648%	$274.4818	$274.48	$274.50	$274.50
Purchase #3	$99.92	12.486%	$112.396	$112.40	$112.40	$112.40
Purchase #4	$245.89	11.572%	$274.3444	$274.34	$274.35	$274.30
Purchase #5	$249.93	8.372%	$270.8541	$270.85	$270.85	$270.90
Purchase #6	$45.72	12.456%	$51.4149	$51.41	$51.40	$51.40
Purchase #7	$73.30	12.576%	$82.5182	$82.52	$82.50	$82.50
7 purchase totals =	$1,123.00		$1,243.5176	$1,243.51	$1,243.50	$1,243.50