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	$246.25	11.108%	$273.6035	$273.60	$273.60	$273.60
Purchase #2	$199.50	7.797%	$215.055	$215.06	$215.05	$215.10
Purchase #3	$113.86	12.700%	$128.3202	$128.32	$128.30	$128.30
Purchase #4	$144.66	9.168%	$157.9224	$157.92	$157.90	$157.90
Purchase #5	$18.48	11.846%	$20.6691	$20.67	$20.65	$20.70
Purchase #6	$137.37	10.221%	$151.4106	$151.41	$151.40	$151.40
Purchase #7	$219.95	3.605%	$227.8792	$227.88	$227.90	$227.90
7 purchase totals =	$1,080.07		$1,174.8600	$1,174.86	$1,174.80	$1,174.90