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	$126.39	3.813%	$131.2093	$131.21	$131.20	$131.20
Purchase #2	$248.36	9.181%	$271.1619	$271.16	$271.15	$271.20
Purchase #3	$113.41	13.115%	$128.2837	$128.28	$128.30	$128.30
Purchase #4	$66.89	5.106%	$70.3054	$70.31	$70.30	$70.30
Purchase #5	$136.31	5.280%	$143.5072	$143.51	$143.50	$143.50
Purchase #6	$84.90	12.458%	$95.4768	$95.48	$95.50	$95.50
Purchase #7	$182.51	6.308%	$194.0227	$194.02	$194.00	$194.00
7 purchase totals =	$958.77		$1,033.9670	$1,033.97	$1,033.95	$1,034.00