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	$239.69	12.359%	$269.3133	$269.31	$269.30	$269.30
Purchase #2	$186.56	6.301%	$198.3151	$198.32	$198.30	$198.30
Purchase #3	$160.46	12.761%	$180.9363	$180.94	$180.95	$180.90
Purchase #4	$23.55	4.320%	$24.5674	$24.57	$24.55	$24.60
Purchase #5	$67.61	3.861%	$70.2204	$70.22	$70.20	$70.20
Purchase #6	$98.48	11.444%	$109.7501	$109.75	$109.75	$109.80
Purchase #7	$108.34	3.632%	$112.2749	$112.27	$112.25	$112.30
7 purchase totals =	$884.69		$965.3775	$965.38	$965.30	$965.40