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	$28.38	9.710%	$31.1357	$31.14	$31.15	$31.10
Purchase #2	$151.92	3.459%	$157.1749	$157.17	$157.15	$157.20
Purchase #3	$144.86	13.215%	$164.0032	$164.00	$164.00	$164.00
Purchase #4	$243.53	10.655%	$269.4781	$269.48	$269.50	$269.50
Purchase #5	$175.48	6.571%	$187.0108	$187.01	$187.00	$187.00
Purchase #6	$97.30	7.379%	$104.4798	$104.48	$104.50	$104.50
Purchase #7	$146.42	11.751%	$163.6258	$163.63	$163.65	$163.60
7 purchase totals =	$987.89		$1,076.9083	$1,076.91	$1,076.95	$1,076.90