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	$105.80	3.214%	$109.2004	$109.20	$109.20	$109.20
Purchase #2	$78.72	13.202%	$89.1126	$89.11	$89.10	$89.10
Purchase #3	$121.51	3.718%	$126.0277	$126.03	$126.05	$126.00
Purchase #4	$60.66	12.614%	$68.3117	$68.31	$68.30	$68.30
Purchase #5	$95.61	5.531%	$100.8982	$100.90	$100.90	$100.90
Purchase #6	$201.39	5.410%	$212.2852	$212.29	$212.30	$212.30
Purchase #7	$164.63	12.437%	$185.105	$185.11	$185.10	$185.10
7 purchase totals =	$828.32		$890.9408	$890.95	$890.95	$890.90