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	$145.33	13.320%	$164.688	$164.69	$164.70	$164.70
Purchase #2	$227.44	8.151%	$245.9786	$245.98	$246.00	$246.00
Purchase #3	$98.59	3.499%	$102.0397	$102.04	$102.05	$102.00
Purchase #4	$248.74	10.111%	$273.8901	$273.89	$273.90	$273.90
Purchase #5	$59.80	13.397%	$67.8114	$67.81	$67.80	$67.80
Purchase #6	$80.49	10.598%	$89.0203	$89.02	$89.00	$89.00
Purchase #7	$31.60	9.187%	$34.5031	$34.50	$34.50	$34.50
7 purchase totals =	$891.99		$977.9312	$977.93	$977.95	$977.90