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	$189.90	6.111%	$201.5048	$201.50	$201.50	$201.50
Purchase #2	$103.89	4.703%	$108.7759	$108.78	$108.80	$108.80
Purchase #3	$128.33	11.323%	$142.8608	$142.86	$142.85	$142.90
Purchase #4	$169.72	8.538%	$184.2107	$184.21	$184.20	$184.20
Purchase #5	$186.76	12.217%	$209.5765	$209.58	$209.60	$209.60
Purchase #6	$198.79	6.858%	$212.423	$212.42	$212.40	$212.40
Purchase #7	$150.80	3.766%	$156.4791	$156.48	$156.50	$156.50
7 purchase totals =	$1,128.19		$1,215.8308	$1,215.83	$1,215.85	$1,215.90