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	$238.75	13.710%	$271.4826	$271.48	$271.50	$271.50
Purchase #2	$136.86	6.174%	$145.3097	$145.31	$145.30	$145.30
Purchase #3	$49.30	12.653%	$55.5379	$55.54	$55.55	$55.50
Purchase #4	$128.73	9.445%	$140.8885	$140.89	$140.90	$140.90
Purchase #5	$163.57	9.316%	$178.8082	$178.81	$178.80	$178.80
Purchase #6	$81.68	4.676%	$85.4994	$85.50	$85.50	$85.50
Purchase #7	$154.38	6.323%	$164.1414	$164.14	$164.15	$164.10
7 purchase totals =	$953.27		$1,041.6677	$1,041.67	$1,041.70	$1,041.60