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	$236.87	13.477%	$268.793	$268.79	$268.80	$268.80
Purchase #2	$98.88	10.599%	$109.3603	$109.36	$109.35	$109.40
Purchase #3	$229.85	13.773%	$261.5072	$261.51	$261.50	$261.50
Purchase #4	$120.81	6.310%	$128.4331	$128.43	$128.45	$128.40
Purchase #5	$163.94	9.850%	$180.0881	$180.09	$180.10	$180.10
Purchase #6	$179.37	5.576%	$189.3717	$189.37	$189.35	$189.40
Purchase #7	$56.82	9.718%	$62.3418	$62.34	$62.35	$62.30
7 purchase totals =	$1,086.54		$1,199.8952	$1,199.89	$1,199.90	$1,199.90